diff --git a/shared/static/scripts/sx-browser.js b/shared/static/scripts/sx-browser.js
index 8966cf7..7b969d9 100644
--- a/shared/static/scripts/sx-browser.js
+++ b/shared/static/scripts/sx-browser.js
@@ -14,7 +14,7 @@
   // =========================================================================
 
   var NIL = Object.freeze({ _nil: true, toString: function() { return "nil"; } });
-  var SX_VERSION = "2026-03-11T21:11:04Z";
+  var SX_VERSION = "2026-03-11T23:22:03Z";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }
@@ -729,10 +729,10 @@
   var args = rest(expr);
   return (isSxTruthy(!isSxTruthy(sxOr((typeOf(head) == "symbol"), (typeOf(head) == "lambda"), (typeOf(head) == "list")))) ? map(function(x) { return trampoline(evalExpr(x, env)); }, expr) : (isSxTruthy((typeOf(head) == "symbol")) ? (function() {
   var name = symbolName(head);
-  return (isSxTruthy((name == "if")) ? sfIf(args, env) : (isSxTruthy((name == "when")) ? sfWhen(args, env) : (isSxTruthy((name == "cond")) ? sfCond(args, env) : (isSxTruthy((name == "case")) ? sfCase(args, env) : (isSxTruthy((name == "and")) ? sfAnd(args, env) : (isSxTruthy((name == "or")) ? sfOr(args, env) : (isSxTruthy((name == "let")) ? sfLet(args, env) : (isSxTruthy((name == "let*")) ? sfLet(args, env) : (isSxTruthy((name == "letrec")) ? sfLetrec(args, env) : (isSxTruthy((name == "lambda")) ? sfLambda(args, env) : (isSxTruthy((name == "fn")) ? sfLambda(args, env) : (isSxTruthy((name == "define")) ? sfDefine(args, env) : (isSxTruthy((name == "defcomp")) ? sfDefcomp(args, env) : (isSxTruthy((name == "defisland")) ? sfDefisland(args, env) : (isSxTruthy((name == "defmacro")) ? sfDefmacro(args, env) : (isSxTruthy((name == "defstyle")) ? sfDefstyle(args, env) : (isSxTruthy((name == "defhandler")) ? sfDefhandler(args, env) : (isSxTruthy((name == "defpage")) ? sfDefpage(args, env) : (isSxTruthy((name == "defquery")) ? sfDefquery(args, env) : (isSxTruthy((name == "defaction")) ? sfDefaction(args, env) : (isSxTruthy((name == "begin")) ? sfBegin(args, env) : (isSxTruthy((name == "do")) ? sfBegin(args, env) : (isSxTruthy((name == "quote")) ? sfQuote(args, env) : (isSxTruthy((name == "quasiquote")) ? sfQuasiquote(args, env) : (isSxTruthy((name == "->")) ? sfThreadFirst(args, env) : (isSxTruthy((name == "set!")) ? sfSetBang(args, env) : (isSxTruthy((name == "reset")) ? sfReset(args, env) : (isSxTruthy((name == "shift")) ? sfShift(args, env) : (isSxTruthy((name == "dynamic-wind")) ? sfDynamicWind(args, env) : (isSxTruthy((name == "map")) ? hoMap(args, env) : (isSxTruthy((name == "map-indexed")) ? hoMapIndexed(args, env) : (isSxTruthy((name == "filter")) ? hoFilter(args, env) : (isSxTruthy((name == "reduce")) ? hoReduce(args, env) : (isSxTruthy((name == "some")) ? hoSome(args, env) : (isSxTruthy((name == "every?")) ? hoEvery(args, env) : (isSxTruthy((name == "for-each")) ? hoForEach(args, env) : (isSxTruthy((isSxTruthy(envHas(env, name)) && isMacro(envGet(env, name)))) ? (function() {
+  return (isSxTruthy((name == "if")) ? sfIf(args, env) : (isSxTruthy((name == "when")) ? sfWhen(args, env) : (isSxTruthy((name == "cond")) ? sfCond(args, env) : (isSxTruthy((name == "case")) ? sfCase(args, env) : (isSxTruthy((name == "and")) ? sfAnd(args, env) : (isSxTruthy((name == "or")) ? sfOr(args, env) : (isSxTruthy((name == "let")) ? sfLet(args, env) : (isSxTruthy((name == "let*")) ? sfLet(args, env) : (isSxTruthy((name == "letrec")) ? sfLetrec(args, env) : (isSxTruthy((name == "lambda")) ? sfLambda(args, env) : (isSxTruthy((name == "fn")) ? sfLambda(args, env) : (isSxTruthy((name == "define")) ? sfDefine(args, env) : (isSxTruthy((name == "defcomp")) ? sfDefcomp(args, env) : (isSxTruthy((name == "defisland")) ? sfDefisland(args, env) : (isSxTruthy((name == "defmacro")) ? sfDefmacro(args, env) : (isSxTruthy((name == "defstyle")) ? sfDefstyle(args, env) : (isSxTruthy((name == "defhandler")) ? sfDefhandler(args, env) : (isSxTruthy((name == "defpage")) ? sfDefpage(args, env) : (isSxTruthy((name == "defquery")) ? sfDefquery(args, env) : (isSxTruthy((name == "defaction")) ? sfDefaction(args, env) : (isSxTruthy((name == "deftype")) ? sfDeftype(args, env) : (isSxTruthy((name == "defeffect")) ? sfDefeffect(args, env) : (isSxTruthy((name == "begin")) ? sfBegin(args, env) : (isSxTruthy((name == "do")) ? sfBegin(args, env) : (isSxTruthy((name == "quote")) ? sfQuote(args, env) : (isSxTruthy((name == "quasiquote")) ? sfQuasiquote(args, env) : (isSxTruthy((name == "->")) ? sfThreadFirst(args, env) : (isSxTruthy((name == "set!")) ? sfSetBang(args, env) : (isSxTruthy((name == "reset")) ? sfReset(args, env) : (isSxTruthy((name == "shift")) ? sfShift(args, env) : (isSxTruthy((name == "dynamic-wind")) ? sfDynamicWind(args, env) : (isSxTruthy((name == "map")) ? hoMap(args, env) : (isSxTruthy((name == "map-indexed")) ? hoMapIndexed(args, env) : (isSxTruthy((name == "filter")) ? hoFilter(args, env) : (isSxTruthy((name == "reduce")) ? hoReduce(args, env) : (isSxTruthy((name == "some")) ? hoSome(args, env) : (isSxTruthy((name == "every?")) ? hoEvery(args, env) : (isSxTruthy((name == "for-each")) ? hoForEach(args, env) : (isSxTruthy((isSxTruthy(envHas(env, name)) && isMacro(envGet(env, name)))) ? (function() {
   var mac = envGet(env, name);
   return makeThunk(expandMacro(mac, args, env), env);
-})() : (isSxTruthy((isSxTruthy(renderActiveP()) && isRenderExpr(expr))) ? renderExpr(expr, env) : evalCall(head, args, env)))))))))))))))))))))))))))))))))))))));
+})() : (isSxTruthy((isSxTruthy(renderActiveP()) && isRenderExpr(expr))) ? renderExpr(expr, env) : evalCall(head, args, env)))))))))))))))))))))))))))))))))))))))));
 })() : evalCall(head, args, env)));
 })(); };
 
@@ -888,11 +888,22 @@ return append_b(inits, nth(binding, 1)); }, bindings) : reduce(function(acc, pai
   // sf-define
   var sfDefine = function(args, env) { return (function() {
   var nameSym = first(args);
-  var value = trampoline(evalExpr(nth(args, 1), env));
+  var hasEffects = (isSxTruthy((len(args) >= 4)) && isSxTruthy((typeOf(nth(args, 1)) == "keyword")) && (keywordName(nth(args, 1)) == "effects"));
+  var valIdx = (isSxTruthy((isSxTruthy((len(args) >= 4)) && isSxTruthy((typeOf(nth(args, 1)) == "keyword")) && (keywordName(nth(args, 1)) == "effects"))) ? 3 : 1);
+  var value = trampoline(evalExpr(nth(args, valIdx), env));
   if (isSxTruthy((isSxTruthy(isLambda(value)) && isNil(lambdaName(value))))) {
   value.name = symbolName(nameSym);
 }
   envSet(env, symbolName(nameSym), value);
+  if (isSxTruthy(hasEffects)) {
+  (function() {
+  var effectsRaw = nth(args, 2);
+  var effectList = (isSxTruthy((typeOf(effectsRaw) == "list")) ? map(function(e) { return (isSxTruthy((typeOf(e) == "symbol")) ? symbolName(e) : (String(e))); }, effectsRaw) : [(String(effectsRaw))]);
+  var effectAnns = (isSxTruthy(envHas(env, "*effect-annotations*")) ? envGet(env, "*effect-annotations*") : {});
+  effectAnns[symbolName(nameSym)] = effectList;
+  return envSet(env, "*effect-annotations*", effectAnns);
+})();
+}
   return value;
 })(); };
 
@@ -909,8 +920,17 @@ return append_b(inits, nth(binding, 1)); }, bindings) : reduce(function(acc, pai
   var affinity = defcompKwarg(args, "affinity", "auto");
   return (function() {
   var comp = makeComponent(compName, params, hasChildren, body, env, affinity);
+  var effects = defcompKwarg(args, "effects", NIL);
   if (isSxTruthy((isSxTruthy(!isSxTruthy(isNil(paramTypes))) && !isSxTruthy(isEmpty(keys(paramTypes)))))) {
   componentSetParamTypes_b(comp, paramTypes);
+}
+  if (isSxTruthy(!isSxTruthy(isNil(effects)))) {
+  (function() {
+  var effectList = (isSxTruthy((typeOf(effects) == "list")) ? map(function(e) { return (isSxTruthy((typeOf(e) == "symbol")) ? symbolName(e) : (String(e))); }, effects) : [(String(effects))]);
+  var effectAnns = (isSxTruthy(envHas(env, "*effect-annotations*")) ? envGet(env, "*effect-annotations*") : {});
+  effectAnns[symbolName(nameSym)] = effectList;
+  return envSet(env, "*effect-annotations*", effectAnns);
+})();
 }
   envSet(env, symbolName(nameSym), comp);
   return comp;
@@ -997,6 +1017,45 @@ return append_b(inits, nth(binding, 1)); }, bindings) : reduce(function(acc, pai
   return value;
 })(); };
 
+  // make-type-def
+  var makeTypeDef = function(name, params, body) { return {"name": name, "params": params, "body": body}; };
+
+  // normalize-type-body
+  var normalizeTypeBody = function(body) { return (isSxTruthy(isNil(body)) ? "nil" : (isSxTruthy((typeOf(body) == "symbol")) ? symbolName(body) : (isSxTruthy((typeOf(body) == "string")) ? body : (isSxTruthy((typeOf(body) == "keyword")) ? keywordName(body) : (isSxTruthy((typeOf(body) == "dict")) ? mapDict(function(k, v) { return normalizeTypeBody(v); }, body) : (isSxTruthy((typeOf(body) == "list")) ? (isSxTruthy(isEmpty(body)) ? "any" : (function() {
+  var head = first(body);
+  return (function() {
+  var headName = (isSxTruthy((typeOf(head) == "symbol")) ? symbolName(head) : (String(head)));
+  return (isSxTruthy((headName == "union")) ? cons("or", map(normalizeTypeBody, rest(body))) : cons(headName, map(normalizeTypeBody, rest(body))));
+})();
+})()) : (String(body)))))))); };
+
+  // sf-deftype
+  var sfDeftype = function(args, env) { return (function() {
+  var nameOrForm = first(args);
+  var bodyExpr = nth(args, 1);
+  var typeName = NIL;
+  var typeParams = [];
+  (isSxTruthy((typeOf(nameOrForm) == "symbol")) ? (typeName = symbolName(nameOrForm)) : (isSxTruthy((typeOf(nameOrForm) == "list")) ? ((typeName = symbolName(first(nameOrForm))), (typeParams = map(function(p) { return (isSxTruthy((typeOf(p) == "symbol")) ? symbolName(p) : (String(p))); }, rest(nameOrForm)))) : NIL));
+  return (function() {
+  var body = normalizeTypeBody(bodyExpr);
+  var registry = (isSxTruthy(envHas(env, "*type-registry*")) ? envGet(env, "*type-registry*") : {});
+  registry[typeName] = makeTypeDef(typeName, typeParams, body);
+  envSet(env, "*type-registry*", registry);
+  return NIL;
+})();
+})(); };
+
+  // sf-defeffect
+  var sfDefeffect = function(args, env) { return (function() {
+  var effectName = (isSxTruthy((typeOf(first(args)) == "symbol")) ? symbolName(first(args)) : (String(first(args))));
+  var registry = (isSxTruthy(envHas(env, "*effect-registry*")) ? envGet(env, "*effect-registry*") : []);
+  if (isSxTruthy(!isSxTruthy(contains(registry, effectName)))) {
+  registry.push(effectName);
+}
+  envSet(env, "*effect-registry*", registry);
+  return NIL;
+})(); };
+
   // sf-begin
   var sfBegin = function(args, env) { return (isSxTruthy(isEmpty(args)) ? NIL : (forEach(function(e) { return trampoline(evalExpr(e, env)); }, slice(args, 0, (len(args) - 1))), makeThunk(last(args), env))); };
 
@@ -1156,7 +1215,7 @@ return append_b(inits, nth(binding, 1)); }, bindings) : reduce(function(acc, pai
   var BOOLEAN_ATTRS = ["async", "autofocus", "autoplay", "checked", "controls", "default", "defer", "disabled", "formnovalidate", "hidden", "inert", "ismap", "loop", "multiple", "muted", "nomodule", "novalidate", "open", "playsinline", "readonly", "required", "reversed", "selected"];
 
   // definition-form?
-  var isDefinitionForm = function(name) { return sxOr((name == "define"), (name == "defcomp"), (name == "defisland"), (name == "defmacro"), (name == "defstyle"), (name == "defhandler")); };
+  var isDefinitionForm = function(name) { return sxOr((name == "define"), (name == "defcomp"), (name == "defisland"), (name == "defmacro"), (name == "defstyle"), (name == "defhandler"), (name == "deftype"), (name == "defeffect")); };
 
   // parse-element-args
   var parseElementArgs = function(args, env) { return (function() {
@@ -1366,7 +1425,7 @@ return (function() { var _m = typeOf(expr); if (_m == "nil") return ""; if (_m =
   var renderValueToHtml = function(val, env) { return (function() { var _m = typeOf(val); if (_m == "nil") return ""; if (_m == "string") return escapeHtml(val); if (_m == "number") return (String(val)); if (_m == "boolean") return (isSxTruthy(val) ? "true" : "false"); if (_m == "list") return renderListToHtml(val, env); if (_m == "raw-html") return rawHtmlContent(val); return escapeHtml((String(val))); })(); };
 
   // RENDER_HTML_FORMS
-  var RENDER_HTML_FORMS = ["if", "when", "cond", "case", "let", "let*", "begin", "do", "define", "defcomp", "defisland", "defmacro", "defstyle", "defhandler", "map", "map-indexed", "filter", "for-each"];
+  var RENDER_HTML_FORMS = ["if", "when", "cond", "case", "let", "let*", "begin", "do", "define", "defcomp", "defisland", "defmacro", "defstyle", "defhandler", "deftype", "defeffect", "map", "map-indexed", "filter", "for-each"];
 
   // render-html-form?
   var isRenderHtmlForm = function(name) { return contains(RENDER_HTML_FORMS, name); };
@@ -1574,7 +1633,7 @@ return (function() { var _m = typeOf(expr); if (_m == "number") return expr; if
 })(); };
 
   // SPECIAL_FORM_NAMES
-  var SPECIAL_FORM_NAMES = ["if", "when", "cond", "case", "and", "or", "let", "let*", "lambda", "fn", "define", "defcomp", "defmacro", "defstyle", "defhandler", "defpage", "defquery", "defaction", "defrelation", "begin", "do", "quote", "quasiquote", "->", "set!", "letrec", "dynamic-wind", "defisland"];
+  var SPECIAL_FORM_NAMES = ["if", "when", "cond", "case", "and", "or", "let", "let*", "lambda", "fn", "define", "defcomp", "defmacro", "defstyle", "defhandler", "defpage", "defquery", "defaction", "defrelation", "begin", "do", "quote", "quasiquote", "->", "set!", "letrec", "dynamic-wind", "defisland", "deftype", "defeffect"];
 
   // HO_FORM_NAMES
   var HO_FORM_NAMES = ["map", "map-indexed", "filter", "reduce", "some", "every?", "for-each"];
@@ -1645,7 +1704,7 @@ return result; }, args);
   return append_b(results, aser(lambdaBody(f), local));
 })() : invoke(f, item)); } }
   return (isSxTruthy(isEmpty(results)) ? NIL : results);
-})() : (isSxTruthy((name == "defisland")) ? (trampoline(evalExpr(expr, env)), serialize(expr)) : (isSxTruthy(sxOr((name == "define"), (name == "defcomp"), (name == "defmacro"), (name == "defstyle"), (name == "defhandler"), (name == "defpage"), (name == "defquery"), (name == "defaction"), (name == "defrelation"))) ? (trampoline(evalExpr(expr, env)), NIL) : trampoline(evalExpr(expr, env)))))))))))))));
+})() : (isSxTruthy((name == "defisland")) ? (trampoline(evalExpr(expr, env)), serialize(expr)) : (isSxTruthy(sxOr((name == "define"), (name == "defcomp"), (name == "defmacro"), (name == "defstyle"), (name == "defhandler"), (name == "defpage"), (name == "defquery"), (name == "defaction"), (name == "defrelation"), (name == "deftype"), (name == "defeffect"))) ? (trampoline(evalExpr(expr, env)), NIL) : trampoline(evalExpr(expr, env)))))))))))))));
 })(); };
 
   // eval-case-aser
@@ -3999,20 +4058,12 @@ return (isSxTruthy((_batchDepth == 0)) ? (function() {
   function domCallMethod() {
     var obj = arguments[0], method = arguments[1];
     var args = Array.prototype.slice.call(arguments, 2);
+    console.log("[sx] dom-call-method:", obj, method, args);
     if (obj && typeof obj[method] === 'function') {
       try { return obj[method].apply(obj, args); }
       catch(e) { console.error("[sx] dom-call-method error:", e); return NIL; }
     }
-    return NIL;
-  }
-  // Post a message to an iframe's contentWindow without exposing the cross-origin
-  // Window object to the SX evaluator (which would trigger _thunk access errors).
-  function domPostMessage(iframe, msg, origin) {
-    try {
-      if (iframe && iframe.contentWindow) {
-        iframe.contentWindow.postMessage(msg, origin || '*');
-      }
-    } catch(e) { console.error("[sx] domPostMessage error:", e); }
+    console.warn("[sx] dom-call-method: method not found or obj null", obj, method);
     return NIL;
   }
 
@@ -5221,7 +5272,6 @@ return (isSxTruthy((_batchDepth == 0)) ? (function() {
   PRIMITIVES["dom-get-prop"] = domGetProp;
   PRIMITIVES["dom-set-prop"] = domSetProp;
   PRIMITIVES["dom-call-method"] = domCallMethod;
-  PRIMITIVES["dom-post-message"] = domPostMessage;
   PRIMITIVES["stop-propagation"] = stopPropagation_;
   PRIMITIVES["error-message"] = errorMessage;
   PRIMITIVES["schedule-idle"] = scheduleIdle;
diff --git a/shared/sx/ref/adapter-async.sx b/shared/sx/ref/adapter-async.sx
index cfcce1b..0922111 100644
--- a/shared/sx/ref/adapter-async.sx
+++ b/shared/sx/ref/adapter-async.sx
@@ -40,7 +40,7 @@
 ;; Async HTML renderer
 ;; --------------------------------------------------------------------------
 
-(define-async async-render
+(define-async async-render :effects [render io]
   (fn (expr (env :as dict) ctx)
     (case (type-of expr)
       "nil"      ""
@@ -56,7 +56,7 @@
       :else      (escape-html (str expr)))))
 
 
-(define-async async-render-list
+(define-async async-render-list :effects [render io]
   (fn (expr (env :as dict) ctx)
     (let ((head (first expr)))
       (if (not (= (type-of head) "symbol"))
@@ -138,7 +138,7 @@
 ;; async-render-raw — handle (raw! ...) in async context
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-raw
+(define-async async-render-raw :effects [render io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((parts (list)))
       (for-each
@@ -157,7 +157,7 @@
 ;; async-render-element — render an HTML element with async arg evaluation
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-element
+(define-async async-render-element :effects [render io]
   (fn ((tag :as string) (args :as list) (env :as dict) ctx)
     (let ((attrs (dict))
           (children (list)))
@@ -185,7 +185,7 @@
 ;; Uses for-each + mutable state instead of reduce, because the bootstrapper
 ;; compiles inline for-each lambdas as for loops (which can contain await).
 
-(define-async async-parse-element-args
+(define-async async-parse-element-args :effects [render io]
   (fn ((args :as list) (attrs :as dict) (children :as list) (env :as dict) ctx)
     (let ((skip false)
           (i 0))
@@ -210,7 +210,7 @@
 ;; async-render-component — expand and render a component asynchronously
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-component
+(define-async async-render-component :effects [render io]
   (fn ((comp :as component) (args :as list) (env :as dict) ctx)
     (let ((kwargs (dict))
           (children (list)))
@@ -232,7 +232,7 @@
 ;; async-render-island — SSR render of reactive island with hydration markers
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-island
+(define-async async-render-island :effects [render io]
   (fn ((island :as island) (args :as list) (env :as dict) ctx)
     (let ((kwargs (dict))
           (children (list)))
@@ -261,7 +261,7 @@
 ;; async-render-lambda — render lambda body in HTML context
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-lambda
+(define-async async-render-lambda :effects [render io]
   (fn ((f :as lambda) (args :as list) (env :as dict) ctx)
     (let ((local (env-merge (lambda-closure f) env)))
       (for-each-indexed
@@ -274,7 +274,7 @@
 ;; async-parse-kw-args — parse keyword args and children with async eval
 ;; --------------------------------------------------------------------------
 
-(define-async async-parse-kw-args
+(define-async async-parse-kw-args :effects [render io]
   (fn ((args :as list) (kwargs :as dict) (children :as list) (env :as dict) ctx)
     (let ((skip false)
           (i 0))
@@ -300,7 +300,7 @@
 ;; --------------------------------------------------------------------------
 ;; Bootstrapper emits this as: [await async_render(x, env, ctx) for x in exprs]
 
-(define-async async-map-render
+(define-async async-map-render :effects [render io]
   (fn ((exprs :as list) (env :as dict) ctx)
     (let ((results (list)))
       (for-each
@@ -316,9 +316,10 @@
 (define ASYNC_RENDER_FORMS
   (list "if" "when" "cond" "case" "let" "let*" "begin" "do"
         "define" "defcomp" "defisland" "defmacro" "defstyle" "defhandler"
+        "deftype" "defeffect"
         "map" "map-indexed" "filter" "for-each"))
 
-(define async-render-form?
+(define async-render-form? :effects []
   (fn ((name :as string))
     (contains? ASYNC_RENDER_FORMS name)))
 
@@ -330,7 +331,7 @@
 ;; Uses cond-scheme? from eval.sx (the FIXED version with every? check)
 ;; and eval-cond from render.sx for correct scheme/clojure classification.
 
-(define-async dispatch-async-render-form
+(define-async dispatch-async-render-form :effects [render io]
   (fn ((name :as string) expr (env :as dict) ctx)
     (cond
       ;; if
@@ -406,7 +407,7 @@
 ;; async-render-cond-scheme — scheme-style cond for render mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-cond-scheme
+(define-async async-render-cond-scheme :effects [render io]
   (fn ((clauses :as list) (env :as dict) ctx)
     (if (empty? clauses)
       ""
@@ -428,7 +429,7 @@
 ;; async-render-cond-clojure — clojure-style cond for render mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-render-cond-clojure
+(define-async async-render-cond-clojure :effects [render io]
   (fn ((clauses :as list) (env :as dict) ctx)
     (if (< (len clauses) 2)
       ""
@@ -448,7 +449,7 @@
 ;; async-process-bindings — evaluate let-bindings asynchronously
 ;; --------------------------------------------------------------------------
 
-(define-async async-process-bindings
+(define-async async-process-bindings :effects [render io]
   (fn (bindings (env :as dict) ctx)
     ;; env-extend (not merge) — Env is not a dict subclass, so merge()
     ;; returns an empty dict, losing all parent scope bindings.
@@ -469,7 +470,7 @@
       local)))
 
 
-(define-async async-process-bindings-flat
+(define-async async-process-bindings-flat :effects [render io]
   (fn ((bindings :as list) (local :as dict) ctx)
     (let ((skip false)
           (i 0))
@@ -494,7 +495,7 @@
 ;; async-map-fn-render — map a lambda/callable over collection for render
 ;; --------------------------------------------------------------------------
 
-(define-async async-map-fn-render
+(define-async async-map-fn-render :effects [render io]
   (fn (f (coll :as list) (env :as dict) ctx)
     (let ((results (list)))
       (for-each
@@ -511,7 +512,7 @@
 ;; async-map-indexed-fn-render — map-indexed variant for render
 ;; --------------------------------------------------------------------------
 
-(define-async async-map-indexed-fn-render
+(define-async async-map-indexed-fn-render :effects [render io]
   (fn (f (coll :as list) (env :as dict) ctx)
     (let ((results (list))
           (i 0))
@@ -530,7 +531,7 @@
 ;; async-invoke — call a native callable, await if coroutine
 ;; --------------------------------------------------------------------------
 
-(define-async async-invoke
+(define-async async-invoke :effects [io]
   (fn (f &rest args)
     (let ((r (apply f args)))
       (if (async-coroutine? r)
@@ -542,7 +543,7 @@
 ;; Async SX wire format (aser)
 ;; ==========================================================================
 
-(define-async async-aser
+(define-async async-aser :effects [render io]
   (fn (expr (env :as dict) ctx)
     (case (type-of expr)
       "number"  expr
@@ -572,7 +573,7 @@
       :else expr)))
 
 
-(define-async async-aser-dict
+(define-async async-aser-dict :effects [render io]
   (fn ((expr :as dict) (env :as dict) ctx)
     (let ((result (dict)))
       (for-each
@@ -586,7 +587,7 @@
 ;; async-aser-list — dispatch on list head for aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-list
+(define-async async-aser-list :effects [render io]
   (fn (expr (env :as dict) ctx)
     (let ((head (first expr))
           (args (rest expr)))
@@ -665,7 +666,7 @@
 ;; async-aser-eval-call — evaluate a function call fully in aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-eval-call
+(define-async async-aser-eval-call :effects [render io]
   (fn (head (args :as list) (env :as dict) ctx)
     (let ((f (async-eval head env ctx))
           (evaled-args (async-eval-args args env ctx)))
@@ -693,7 +694,7 @@
 ;; async-eval-args — evaluate a list of args asynchronously
 ;; --------------------------------------------------------------------------
 
-(define-async async-eval-args
+(define-async async-eval-args :effects [io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((results (list)))
       (for-each
@@ -706,7 +707,7 @@
 ;; async-aser-map-list — aser each element of a list
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-map-list
+(define-async async-aser-map-list :effects [render io]
   (fn ((exprs :as list) (env :as dict) ctx)
     (let ((results (list)))
       (for-each
@@ -719,7 +720,7 @@
 ;; async-aser-fragment — serialize (<> child1 child2 ...) in aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-fragment
+(define-async async-aser-fragment :effects [render io]
   (fn ((children :as list) (env :as dict) ctx)
     (let ((parts (list)))
       (for-each
@@ -743,7 +744,7 @@
 ;; async-aser-component — expand component server-side in aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-component
+(define-async async-aser-component :effects [render io]
   (fn ((comp :as component) (args :as list) (env :as dict) ctx)
     (let ((kwargs (dict))
           (children (list)))
@@ -775,7 +776,7 @@
 ;; async-parse-aser-kw-args — parse keyword args for aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-parse-aser-kw-args
+(define-async async-parse-aser-kw-args :effects [render io]
   (fn ((args :as list) (kwargs :as dict) (children :as list) (env :as dict) ctx)
     (let ((skip false)
           (i 0))
@@ -800,7 +801,7 @@
 ;; async-aser-call — serialize an SX call (tag or component) in aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-call
+(define-async async-aser-call :effects [render io]
   (fn ((name :as string) (args :as list) (env :as dict) ctx)
     (let ((token (if (or (= name "svg") (= name "math"))
                    (svg-context-set! true)
@@ -853,12 +854,13 @@
         "let" "let*" "lambda" "fn"
         "define" "defcomp" "defmacro" "defstyle"
         "defhandler" "defpage" "defquery" "defaction"
-        "begin" "do" "quote" "->" "set!" "defisland"))
+        "begin" "do" "quote" "->" "set!" "defisland"
+        "deftype" "defeffect"))
 
 (define ASYNC_ASER_HO_NAMES
   (list "map" "map-indexed" "filter" "for-each"))
 
-(define async-aser-form?
+(define async-aser-form? :effects []
   (fn ((name :as string))
     (or (contains? ASYNC_ASER_FORM_NAMES name)
         (contains? ASYNC_ASER_HO_NAMES name))))
@@ -870,7 +872,7 @@
 ;;
 ;; Uses cond-scheme? from eval.sx (the FIXED version with every? check).
 
-(define-async dispatch-async-aser-form
+(define-async dispatch-async-aser-form :effects [render io]
   (fn ((name :as string) expr (env :as dict) ctx)
     (let ((args (rest expr)))
       (cond
@@ -987,7 +989,8 @@
         ;; Definition forms — evaluate for side effects
         (or (= name "define") (= name "defcomp") (= name "defmacro")
             (= name "defstyle") (= name "defhandler") (= name "defpage")
-            (= name "defquery") (= name "defaction"))
+            (= name "defquery") (= name "defaction")
+            (= name "deftype") (= name "defeffect"))
           (do (async-eval expr env ctx) nil)
 
         ;; Fallback
@@ -999,7 +1002,7 @@
 ;; async-aser-cond-scheme — scheme-style cond for aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-cond-scheme
+(define-async async-aser-cond-scheme :effects [render io]
   (fn ((clauses :as list) (env :as dict) ctx)
     (if (empty? clauses)
       nil
@@ -1021,7 +1024,7 @@
 ;; async-aser-cond-clojure — clojure-style cond for aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-cond-clojure
+(define-async async-aser-cond-clojure :effects [render io]
   (fn ((clauses :as list) (env :as dict) ctx)
     (if (< (len clauses) 2)
       nil
@@ -1041,7 +1044,7 @@
 ;; async-aser-case-loop — case dispatch for aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-case-loop
+(define-async async-aser-case-loop :effects [render io]
   (fn (match-val (clauses :as list) (env :as dict) ctx)
     (if (< (len clauses) 2)
       nil
@@ -1061,7 +1064,7 @@
 ;; async-aser-thread-first — -> form in aser mode
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-thread-first
+(define-async async-aser-thread-first :effects [render io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((result (async-eval (first args) env ctx)))
       (for-each
@@ -1081,7 +1084,7 @@
 ;; async-invoke-or-lambda — invoke a callable or lambda with args
 ;; --------------------------------------------------------------------------
 
-(define-async async-invoke-or-lambda
+(define-async async-invoke-or-lambda :effects [render io]
   (fn (f (args :as list) (env :as dict) ctx)
     (cond
       (and (callable? f) (not (lambda? f)) (not (component? f)))
@@ -1103,7 +1106,7 @@
 ;; Async aser HO forms (map, map-indexed, for-each)
 ;; --------------------------------------------------------------------------
 
-(define-async async-aser-ho-map
+(define-async async-aser-ho-map :effects [render io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((f (async-eval (first args) env ctx))
           (coll (async-eval (nth args 1) env ctx))
@@ -1119,7 +1122,7 @@
       results)))
 
 
-(define-async async-aser-ho-map-indexed
+(define-async async-aser-ho-map-indexed :effects [render io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((f (async-eval (first args) env ctx))
           (coll (async-eval (nth args 1) env ctx))
@@ -1138,7 +1141,7 @@
       results)))
 
 
-(define-async async-aser-ho-for-each
+(define-async async-aser-ho-for-each :effects [render io]
   (fn ((args :as list) (env :as dict) ctx)
     (let ((f (async-eval (first args) env ctx))
           (coll (async-eval (nth args 1) env ctx))
@@ -1169,7 +1172,7 @@
 ;;   (sx-expr? x)             — check if SxExpr
 ;;   (set-expand-components!) — enable component expansion context var
 
-(define-async async-eval-slot-inner
+(define-async async-eval-slot-inner :effects [render io]
   (fn (expr (env :as dict) ctx)
     ;; NOTE: Uses statement-form let + set! to avoid expression-context
     ;; let (IIFE lambdas) which can't contain await in Python.
@@ -1195,7 +1198,7 @@
             (make-sx-expr (serialize result))))))))
 
 
-(define-async async-maybe-expand-result
+(define-async async-maybe-expand-result :effects [render io]
   (fn (result (env :as dict) ctx)
     ;; If the aser result is a component call string like "(~foo ...)",
     ;; re-parse and expand it. This handles indirect component references
diff --git a/shared/sx/ref/adapter-dom.sx b/shared/sx/ref/adapter-dom.sx
index 5ff0b53..8c00e92 100644
--- a/shared/sx/ref/adapter-dom.sx
+++ b/shared/sx/ref/adapter-dom.sx
@@ -18,7 +18,7 @@
 ;; render-to-dom — main entry point
 ;; --------------------------------------------------------------------------
 
-(define render-to-dom
+(define render-to-dom :effects [render]
   (fn (expr (env :as dict) (ns :as string))
     (set-render-active! true)
     (case (type-of expr)
@@ -66,7 +66,7 @@
 ;; render-dom-list — dispatch on list head
 ;; --------------------------------------------------------------------------
 
-(define render-dom-list
+(define render-dom-list :effects [render]
   (fn (expr (env :as dict) (ns :as string))
     (let ((head (first expr)))
       (cond
@@ -165,7 +165,7 @@
 ;; render-dom-element — create a DOM element with attrs and children
 ;; --------------------------------------------------------------------------
 
-(define render-dom-element
+(define render-dom-element :effects [render]
   (fn ((tag :as string) (args :as list) (env :as dict) (ns :as string))
     ;; Detect namespace from tag
     (let ((new-ns (cond (= tag "svg") SVG_NS
@@ -236,7 +236,7 @@
 ;; render-dom-component — expand and render a component
 ;; --------------------------------------------------------------------------
 
-(define render-dom-component
+(define render-dom-component :effects [render]
   (fn ((comp :as component) (args :as list) (env :as dict) (ns :as string))
     ;; Parse kwargs and children, bind into component env, render body.
     (let ((kwargs (dict))
@@ -283,7 +283,7 @@
 ;; render-dom-fragment — render children into a DocumentFragment
 ;; --------------------------------------------------------------------------
 
-(define render-dom-fragment
+(define render-dom-fragment :effects [render]
   (fn ((args :as list) (env :as dict) (ns :as string))
     (let ((frag (create-fragment)))
       (for-each
@@ -296,7 +296,7 @@
 ;; render-dom-raw — insert unescaped content
 ;; --------------------------------------------------------------------------
 
-(define render-dom-raw
+(define render-dom-raw :effects [render]
   (fn ((args :as list) (env :as dict))
     (let ((frag (create-fragment)))
       (for-each
@@ -317,7 +317,7 @@
 ;; render-dom-unknown-component — visible warning element
 ;; --------------------------------------------------------------------------
 
-(define render-dom-unknown-component
+(define render-dom-unknown-component :effects [render]
   (fn ((name :as string))
     (error (str "Unknown component: " name))))
 
@@ -334,11 +334,11 @@
         "map" "map-indexed" "filter" "for-each" "portal"
         "error-boundary"))
 
-(define render-dom-form?
+(define render-dom-form? :effects []
   (fn ((name :as string))
     (contains? RENDER_DOM_FORMS name)))
 
-(define dispatch-render-form
+(define dispatch-render-form :effects [render]
   (fn ((name :as string) expr (env :as dict) (ns :as string))
     (cond
       ;; if — reactive inside islands (re-renders when signal deps change)
@@ -580,7 +580,7 @@
 ;; render-lambda-dom — render a lambda body in DOM context
 ;; --------------------------------------------------------------------------
 
-(define render-lambda-dom
+(define render-lambda-dom :effects [render]
   (fn ((f :as lambda) (args :as list) (env :as dict) (ns :as string))
     ;; Bind lambda params and render body as DOM
     (let ((local (env-merge (lambda-closure f) env)))
@@ -604,7 +604,7 @@
 ;;   - Attribute bindings: (deref sig) in attr → reactive attribute
 ;;   - Conditional fragments: (when (deref sig) ...) → reactive show/hide
 
-(define render-dom-island
+(define render-dom-island :effects [render mutation]
   (fn ((island :as island) (args :as list) (env :as dict) (ns :as string))
     ;; Parse kwargs and children (same as component)
     (let ((kwargs (dict))
@@ -678,7 +678,7 @@
 ;;
 ;; Supports :tag keyword to change wrapper element (default "div").
 
-(define render-dom-lake
+(define render-dom-lake :effects [render]
   (fn ((args :as list) (env :as dict) (ns :as string))
     (let ((lake-id nil)
           (lake-tag "div")
@@ -722,7 +722,7 @@
 ;; Renders as <div data-sx-marsh="name">children</div>.
 ;; Stores the island env and transform on the element for morph retrieval.
 
-(define render-dom-marsh
+(define render-dom-marsh :effects [render]
   (fn ((args :as list) (env :as dict) (ns :as string))
     (let ((marsh-id nil)
           (marsh-tag "div")
@@ -769,7 +769,7 @@
 
 ;; reactive-text — create a text node bound to a signal
 ;; Used when (deref sig) appears in a text position inside an island.
-(define reactive-text
+(define reactive-text :effects [render mutation]
   (fn (sig)
     (let ((node (create-text-node (str (deref sig)))))
       (effect (fn ()
@@ -780,7 +780,7 @@
 ;; Used when an attribute value contains (deref sig) inside an island.
 ;; Marks the attribute name on the element via data-sx-reactive-attrs so
 ;; the morph algorithm knows not to overwrite it with server content.
-(define reactive-attr
+(define reactive-attr :effects [render mutation]
   (fn (el (attr-name :as string) (compute-fn :as lambda))
     ;; Mark this attribute as reactively managed
     (let ((existing (or (dom-get-attr el "data-sx-reactive-attrs") ""))
@@ -801,7 +801,7 @@
 
 ;; reactive-fragment — conditionally render a fragment based on a signal
 ;; Used for (when (deref sig) ...) or (if (deref sig) ...) inside an island.
-(define reactive-fragment
+(define reactive-fragment :effects [render mutation]
   (fn ((test-fn :as lambda) (render-fn :as lambda) (env :as dict) (ns :as string))
     (let ((marker (create-comment "island-fragment"))
           (current-nodes (list)))
@@ -823,13 +823,13 @@
 ;; existing DOM nodes are reused across updates. Only additions, removals,
 ;; and reorderings touch the DOM. Without keys, falls back to clear+rerender.
 
-(define render-list-item
+(define render-list-item :effects [render]
   (fn ((map-fn :as lambda) item (env :as dict) (ns :as string))
     (if (lambda? map-fn)
       (render-lambda-dom map-fn (list item) env ns)
       (render-to-dom (apply map-fn (list item)) env ns))))
 
-(define extract-key
+(define extract-key :effects [render]
   (fn (node (index :as number))
     ;; Extract key from rendered node: :key attr, data-key, or index fallback
     (let ((k (dom-get-attr node "key")))
@@ -838,7 +838,7 @@
         (let ((dk (dom-get-data node "key")))
           (if dk (str dk) (str "__idx_" index)))))))
 
-(define reactive-list
+(define reactive-list :effects [render mutation]
   (fn ((map-fn :as lambda) (items-sig :as signal) (env :as dict) (ns :as string))
     (let ((container (create-fragment))
           (marker (create-comment "island-list"))
@@ -924,7 +924,7 @@
 ;;
 ;; Handles: input[text/number/email/...], textarea, select, checkbox, radio
 
-(define bind-input
+(define bind-input :effects [render mutation]
   (fn (el (sig :as signal))
     (let ((input-type (lower (or (dom-get-attr el "type") "")))
           (is-checkbox (or (= input-type "checkbox")
@@ -959,7 +959,7 @@
 ;; position. Registers a disposer to clean up portal content on island
 ;; teardown.
 
-(define render-dom-portal
+(define render-dom-portal :effects [render]
   (fn ((args :as list) (env :as dict) (ns :as string))
     (let ((selector (trampoline (eval-expr (first args) env)))
           (target (or (dom-query selector)
@@ -999,7 +999,7 @@
 ;;   (fn (err retry) ...)
 ;; Calling (retry) re-renders the body, replacing the fallback.
 
-(define render-dom-error-boundary
+(define render-dom-error-boundary :effects [render]
   (fn ((args :as list) (env :as dict) (ns :as string))
     (let ((fallback-expr (first args))
           (body-exprs (rest args))
diff --git a/shared/sx/ref/adapter-html.sx b/shared/sx/ref/adapter-html.sx
index 306baaf..368dd89 100644
--- a/shared/sx/ref/adapter-html.sx
+++ b/shared/sx/ref/adapter-html.sx
@@ -13,7 +13,7 @@
 ;; ==========================================================================
 
 
-(define render-to-html
+(define render-to-html :effects [render]
   (fn (expr (env :as dict))
     (set-render-active! true)
     (case (type-of expr)
@@ -33,7 +33,7 @@
       ;; Everything else — evaluate first
       :else     (render-value-to-html (trampoline (eval-expr expr env)) env))))
 
-(define render-value-to-html
+(define render-value-to-html :effects [render]
   (fn (val (env :as dict))
     (case (type-of val)
       "nil"     ""
@@ -52,9 +52,10 @@
 (define RENDER_HTML_FORMS
   (list "if" "when" "cond" "case" "let" "let*" "begin" "do"
         "define" "defcomp" "defisland" "defmacro" "defstyle" "defhandler"
+        "deftype" "defeffect"
         "map" "map-indexed" "filter" "for-each"))
 
-(define render-html-form?
+(define render-html-form? :effects []
   (fn ((name :as string))
     (contains? RENDER_HTML_FORMS name)))
 
@@ -63,7 +64,7 @@
 ;; render-list-to-html — dispatch on list head
 ;; --------------------------------------------------------------------------
 
-(define render-list-to-html
+(define render-list-to-html :effects [render]
   (fn ((expr :as list) (env :as dict))
     (if (empty? expr)
       ""
@@ -134,7 +135,7 @@
 ;; dispatch-html-form — render-aware special form handling for HTML output
 ;; --------------------------------------------------------------------------
 
-(define dispatch-html-form
+(define dispatch-html-form :effects [render]
   (fn ((name :as string) (expr :as list) (env :as dict))
     (cond
       ;; if
@@ -234,7 +235,7 @@
 ;; render-lambda-html — render a lambda body in HTML context
 ;; --------------------------------------------------------------------------
 
-(define render-lambda-html
+(define render-lambda-html :effects [render]
   (fn ((f :as lambda) (args :as list) (env :as dict))
     (let ((local (env-merge (lambda-closure f) env)))
       (for-each-indexed
@@ -248,7 +249,7 @@
 ;; render-html-component — expand and render a component
 ;; --------------------------------------------------------------------------
 
-(define render-html-component
+(define render-html-component :effects [render]
   (fn ((comp :as component) (args :as list) (env :as dict))
     ;; Expand component and render body through HTML adapter.
     ;; Component body contains rendering forms (HTML tags) that only the
@@ -287,7 +288,7 @@
         (render-to-html (component-body comp) local)))))
 
 
-(define render-html-element
+(define render-html-element :effects [render]
   (fn ((tag :as string) (args :as list) (env :as dict))
     (let ((parsed (parse-element-args args env))
           (attrs  (first parsed))
@@ -311,7 +312,7 @@
 ;; Lakes are server territory inside islands. The morph can update lake
 ;; content while preserving surrounding reactive DOM.
 
-(define render-html-lake
+(define render-html-lake :effects [render]
   (fn ((args :as list) (env :as dict))
     (let ((lake-id nil)
           (lake-tag "div")
@@ -350,7 +351,7 @@
 ;; re-evaluated in the island's signal scope. Server renders children normally;
 ;; the :transform is a client-only concern.
 
-(define render-html-marsh
+(define render-html-marsh :effects [render]
   (fn ((args :as list) (env :as dict))
     (let ((marsh-id nil)
           (marsh-tag "div")
@@ -393,7 +394,7 @@
 ;;   (reset! s v) → no-op
 ;;   (swap! s f)  → no-op
 
-(define render-html-island
+(define render-html-island :effects [render]
   (fn ((island :as island) (args :as list) (env :as dict))
     ;; Parse kwargs and children (same pattern as render-html-component)
     (let ((kwargs (dict))
@@ -451,7 +452,7 @@
 ;; Uses the SX serializer (not JSON) so the client can parse with sx-parse.
 ;; Handles all SX types natively: numbers, strings, booleans, nil, lists, dicts.
 
-(define serialize-island-state
+(define serialize-island-state :effects []
   (fn ((kwargs :as dict))
     (if (empty-dict? kwargs)
       nil
diff --git a/shared/sx/ref/adapter-sx.sx b/shared/sx/ref/adapter-sx.sx
index 2979ecb..f55da20 100644
--- a/shared/sx/ref/adapter-sx.sx
+++ b/shared/sx/ref/adapter-sx.sx
@@ -11,7 +11,7 @@
 ;; ==========================================================================
 
 
-(define render-to-sx
+(define render-to-sx :effects [render]
   (fn (expr (env :as dict))
     (let ((result (aser expr env)))
       ;; aser-call already returns serialized SX strings;
@@ -20,8 +20,8 @@
         result
         (serialize result)))))
 
-(define aser
-  (fn (expr (env :as dict))
+(define aser :effects [render]
+  (fn ((expr :as any) (env :as dict))
     ;; Evaluate for SX wire format — serialize rendering forms,
     ;; evaluate control flow and function calls.
     (set-render-active! true)
@@ -51,7 +51,7 @@
       :else expr)))
 
 
-(define aser-list
+(define aser-list :effects [render]
   (fn ((expr :as list) (env :as dict))
     (let ((head (first expr))
           (args (rest expr)))
@@ -103,7 +103,7 @@
                   :else (error (str "Not callable: " (inspect f)))))))))))
 
 
-(define aser-fragment
+(define aser-fragment :effects [render]
   (fn ((children :as list) (env :as dict))
     ;; Serialize (<> child1 child2 ...) to sx source string
     ;; Must flatten list results (e.g. from map/filter) to avoid nested parens
@@ -125,7 +125,7 @@
         (str "(<> " (join " " parts) ")")))))
 
 
-(define aser-call
+(define aser-call :effects [render]
   (fn ((name :as string) (args :as list) (env :as dict))
     ;; Serialize (name :key val child ...) — evaluate args but keep as sx
     ;; Uses for-each + mutable state (not reduce) so bootstrapper emits for-loops
@@ -170,17 +170,18 @@
         "define" "defcomp" "defmacro" "defstyle"
         "defhandler" "defpage" "defquery" "defaction" "defrelation"
         "begin" "do" "quote" "quasiquote"
-        "->" "set!" "letrec" "dynamic-wind" "defisland"))
+        "->" "set!" "letrec" "dynamic-wind" "defisland"
+        "deftype" "defeffect"))
 
 (define HO_FORM_NAMES
   (list "map" "map-indexed" "filter" "reduce"
         "some" "every?" "for-each"))
 
-(define special-form?
+(define special-form? :effects []
   (fn ((name :as string))
     (contains? SPECIAL_FORM_NAMES name)))
 
-(define ho-form?
+(define ho-form? :effects []
   (fn ((name :as string))
     (contains? HO_FORM_NAMES name)))
 
@@ -193,7 +194,7 @@
 ;; through aser (serializing tags/components instead of rendering HTML).
 ;; Definition forms evaluate for side effects and return nil.
 
-(define aser-special
+(define aser-special :effects [render]
   (fn ((name :as string) (expr :as list) (env :as dict))
     (let ((args (rest expr)))
       (cond
@@ -304,7 +305,8 @@
         ;; Definition forms — evaluate for side effects
         (or (= name "define") (= name "defcomp") (= name "defmacro")
             (= name "defstyle") (= name "defhandler") (= name "defpage")
-            (= name "defquery") (= name "defaction") (= name "defrelation"))
+            (= name "defquery") (= name "defaction") (= name "defrelation")
+            (= name "deftype") (= name "defeffect"))
           (do (trampoline (eval-expr expr env)) nil)
 
         ;; Everything else — evaluate normally
@@ -313,7 +315,7 @@
 
 
 ;; Helper: case dispatch for aser mode
-(define eval-case-aser
+(define eval-case-aser :effects [render]
   (fn (match-val (clauses :as list) (env :as dict))
     (if (< (len clauses) 2)
       nil
diff --git a/shared/sx/ref/boot.sx b/shared/sx/ref/boot.sx
index 494bbf4..aca976a 100644
--- a/shared/sx/ref/boot.sx
+++ b/shared/sx/ref/boot.sx
@@ -26,7 +26,7 @@
 (define HEAD_HOIST_SELECTOR
   "meta, title, link[rel='canonical'], script[type='application/ld+json']")
 
-(define hoist-head-elements-full
+(define hoist-head-elements-full :effects [mutation io]
   (fn (root)
     (let ((els (dom-query-all root HEAD_HOIST_SELECTOR)))
       (for-each
@@ -71,7 +71,7 @@
 ;; Mount — render SX source into a DOM element
 ;; --------------------------------------------------------------------------
 
-(define sx-mount
+(define sx-mount :effects [mutation io]
   (fn (target (source :as string) (extra-env :as dict))
     ;; Render SX source string into target element.
     ;; target: Element or CSS selector string
@@ -100,7 +100,7 @@
 ;; Finds the suspense wrapper by data-suspense attribute, renders the
 ;; new SX content, and replaces the wrapper's children.
 
-(define resolve-suspense
+(define resolve-suspense :effects [mutation io]
   (fn ((id :as string) (sx :as string))
     ;; Process any new <script type="text/sx"> tags that arrived via
     ;; streaming (e.g. extra component defs) before resolving.
@@ -127,7 +127,7 @@
 ;; Hydrate — render all [data-sx] elements
 ;; --------------------------------------------------------------------------
 
-(define sx-hydrate-elements
+(define sx-hydrate-elements :effects [mutation io]
   (fn (root)
     ;; Find all [data-sx] elements within root and render them.
     (let ((els (dom-query-all (or root (dom-body)) "[data-sx]")))
@@ -143,7 +143,7 @@
 ;; Update — re-render a [data-sx] element with new env data
 ;; --------------------------------------------------------------------------
 
-(define sx-update-element
+(define sx-update-element :effects [mutation io]
   (fn (el new-env)
     ;; Re-render a [data-sx] element.
     ;; Reads source from data-sx attr, base env from data-sx-env attr.
@@ -165,7 +165,7 @@
 ;; Render component — build synthetic call from kwargs dict
 ;; --------------------------------------------------------------------------
 
-(define sx-render-component
+(define sx-render-component :effects [mutation io]
   (fn ((name :as string) (kwargs :as dict) (extra-env :as dict))
     ;; Render a named component with keyword args.
     ;; name: component name (with or without ~ prefix)
@@ -190,7 +190,7 @@
 ;; Script processing — <script type="text/sx">
 ;; --------------------------------------------------------------------------
 
-(define process-sx-scripts
+(define process-sx-scripts :effects [mutation io]
   (fn (root)
     ;; Process all <script type="text/sx"> tags.
     ;; - data-components + data-hash → localStorage cache
@@ -235,7 +235,7 @@
 ;; Component script with caching
 ;; --------------------------------------------------------------------------
 
-(define process-component-script
+(define process-component-script :effects [mutation io]
   (fn (script (text :as string))
     ;; Handle <script type="text/sx" data-components data-hash="...">
     (let ((hash (dom-get-attr script "data-hash")))
@@ -288,7 +288,7 @@
 
 (define _page-routes (list))
 
-(define process-page-scripts
+(define process-page-scripts :effects [mutation io]
   (fn ()
     ;; Process <script type="text/sx-pages"> tags.
     ;; Parses SX page registry and builds route entries with parsed patterns.
@@ -331,7 +331,7 @@
 ;; 5. Morph existing DOM to preserve structure, focus, scroll
 ;; 6. Store disposers on the element for cleanup
 
-(define sx-hydrate-islands
+(define sx-hydrate-islands :effects [mutation io]
   (fn (root)
     (let ((els (dom-query-all (or root (dom-body)) "[data-sx-island]")))
       (for-each
@@ -341,7 +341,7 @@
             (hydrate-island el)))
         els))))
 
-(define hydrate-island
+(define hydrate-island :effects [mutation io]
   (fn (el)
     (let ((name (dom-get-attr el "data-sx-island"))
           (state-sx (or (dom-get-attr el "data-sx-state") "{}")))
@@ -388,7 +388,7 @@
 ;; Island disposal — clean up when island removed from DOM
 ;; --------------------------------------------------------------------------
 
-(define dispose-island
+(define dispose-island :effects [mutation io]
   (fn (el)
     (let ((disposers (dom-get-data el "sx-disposers")))
       (when disposers
@@ -398,7 +398,7 @@
           disposers)
         (dom-set-data el "sx-disposers" nil)))))
 
-(define dispose-islands-in
+(define dispose-islands-in :effects [mutation io]
   (fn (root)
     ;; Dispose islands within root, but SKIP hydrated islands —
     ;; they may be preserved across morphs. Only dispose islands
@@ -419,7 +419,7 @@
 ;; Full boot sequence
 ;; --------------------------------------------------------------------------
 
-(define boot-init
+(define boot-init :effects [mutation io]
   (fn ()
     ;; Full browser initialization:
     ;; 1. CSS tracking
diff --git a/shared/sx/ref/bootstrap_py.py b/shared/sx/ref/bootstrap_py.py
index eb2e342..b84010b 100644
--- a/shared/sx/ref/bootstrap_py.py
+++ b/shared/sx/ref/bootstrap_py.py
@@ -664,7 +664,12 @@ class PyEmitter:
     def _emit_define(self, expr, indent: int = 0) -> str:
         pad = "    " * indent
         name = expr[1].name if isinstance(expr[1], Symbol) else str(expr[1])
-        val_expr = expr[2]
+        # Handle (define name :effects [...] value) — skip :effects annotation
+        if (len(expr) >= 5 and isinstance(expr[2], Keyword)
+                and expr[2].name == "effects"):
+            val_expr = expr[4]
+        else:
+            val_expr = expr[2]
         # Always emit fn-bodied defines as def statements for flat control flow
         if (isinstance(val_expr, list) and val_expr and
                 isinstance(val_expr[0], Symbol) and val_expr[0].name in ("fn", "lambda")):
@@ -675,7 +680,12 @@ class PyEmitter:
     def _emit_define_async(self, expr, indent: int = 0) -> str:
         """Emit a define-async form as an async def statement."""
         name = expr[1].name if isinstance(expr[1], Symbol) else str(expr[1])
-        val_expr = expr[2]
+        # Handle (define-async name :effects [...] value) — skip :effects annotation
+        if (len(expr) >= 5 and isinstance(expr[2], Keyword)
+                and expr[2].name == "effects"):
+            val_expr = expr[4]
+        else:
+            val_expr = expr[2]
         if (isinstance(val_expr, list) and val_expr and
                 isinstance(val_expr[0], Symbol) and val_expr[0].name in ("fn", "lambda")):
             return self._emit_define_as_def(name, val_expr, indent, is_async=True)
diff --git a/shared/sx/ref/boundary.sx b/shared/sx/ref/boundary.sx
index 32c2d08..5680b1c 100644
--- a/shared/sx/ref/boundary.sx
+++ b/shared/sx/ref/boundary.sx
@@ -12,6 +12,7 @@
 ;;   (define-io-primitive "name"
 ;;     :params (param1 param2 &key ...)
 ;;     :returns "type"
+;;     :effects [io]
 ;;     :async true
 ;;     :doc "description"
 ;;     :context :request)
@@ -38,6 +39,7 @@
 (define-io-primitive "current-user"
   :params ()
   :returns "dict?"
+  :effects [io]
   :async true
   :doc "Current authenticated user dict, or nil."
   :context :request)
@@ -45,6 +47,7 @@
 (define-io-primitive "request-arg"
   :params (name &rest default)
   :returns "any"
+  :effects [io]
   :async true
   :doc "Read a query string argument from the current request."
   :context :request)
@@ -52,6 +55,7 @@
 (define-io-primitive "request-path"
   :params ()
   :returns "string"
+  :effects [io]
   :async true
   :doc "Current request path."
   :context :request)
@@ -59,6 +63,7 @@
 (define-io-primitive "request-view-args"
   :params (key)
   :returns "any"
+  :effects [io]
   :async true
   :doc "Read a URL view argument from the current request."
   :context :request)
@@ -66,6 +71,7 @@
 (define-io-primitive "csrf-token"
   :params ()
   :returns "string"
+  :effects [io]
   :async true
   :doc "Current CSRF token string."
   :context :request)
@@ -73,6 +79,7 @@
 (define-io-primitive "abort"
   :params (status &rest message)
   :returns "nil"
+  :effects [io]
   :async true
   :doc "Raise HTTP error from SX."
   :context :request)
@@ -82,6 +89,7 @@
 (define-io-primitive "url-for"
   :params (endpoint &key)
   :returns "string"
+  :effects [io]
   :async true
   :doc "Generate URL for a named endpoint."
   :context :request)
@@ -89,6 +97,7 @@
 (define-io-primitive "route-prefix"
   :params ()
   :returns "string"
+  :effects [io]
   :async true
   :doc "Service URL prefix for dev/prod routing."
   :context :request)
@@ -98,6 +107,7 @@
 (define-io-primitive "app-url"
   :params (service &rest path)
   :returns "string"
+  :effects [io]
   :async false
   :doc "Full URL for a service: (app-url \"blog\" \"/my-post/\")."
   :context :config)
@@ -105,6 +115,7 @@
 (define-io-primitive "asset-url"
   :params (&rest path)
   :returns "string"
+  :effects [io]
   :async false
   :doc "Versioned static asset URL."
   :context :config)
@@ -112,6 +123,7 @@
 (define-io-primitive "config"
   :params (key)
   :returns "any"
+  :effects [io]
   :async false
   :doc "Read a value from host configuration."
   :context :config)
@@ -138,11 +150,13 @@
 (declare-signal-primitive "signal"
   :params (initial-value)
   :returns "signal"
+  :effects []
   :doc "Create a reactive signal container with an initial value.")
 
 (declare-signal-primitive "deref"
   :params (signal)
   :returns "any"
+  :effects []
   :doc "Read a signal's current value. In a reactive context (inside an island),
         subscribes the current DOM binding to the signal. Outside reactive
         context, just returns the value.")
@@ -150,23 +164,27 @@
 (declare-signal-primitive "reset!"
   :params (signal value)
   :returns "nil"
+  :effects [mutation]
   :doc "Set a signal to a new value. Notifies all subscribers.")
 
 (declare-signal-primitive "swap!"
   :params (signal f &rest args)
   :returns "nil"
+  :effects [mutation]
   :doc "Update a signal by applying f to its current value. (swap! s inc)
         is equivalent to (reset! s (inc (deref s))) but atomic.")
 
 (declare-signal-primitive "computed"
   :params (compute-fn)
   :returns "signal"
+  :effects []
   :doc "Create a derived signal that recomputes when its dependencies change.
         Dependencies are discovered automatically by tracking deref calls.")
 
 (declare-signal-primitive "effect"
   :params (effect-fn)
   :returns "lambda"
+  :effects [mutation]
   :doc "Run a side effect that re-runs when its signal dependencies change.
         Returns a dispose function. If the effect function returns a function,
         it is called as cleanup before the next run.")
@@ -174,5 +192,6 @@
 (declare-signal-primitive "batch"
   :params (thunk)
   :returns "any"
+  :effects [mutation]
   :doc "Group multiple signal writes. Subscribers are notified once at the end,
         after all values have been updated.")
diff --git a/shared/sx/ref/deps.sx b/shared/sx/ref/deps.sx
index fd66a26..b52a62e 100644
--- a/shared/sx/ref/deps.sx
+++ b/shared/sx/ref/deps.sx
@@ -31,14 +31,14 @@
 ;; Walks all branches of control flow (if/when/cond/case) to find
 ;; every component that *could* be rendered.
 
-(define scan-refs
+(define scan-refs :effects []
   (fn (node)
     (let ((refs (list)))
       (scan-refs-walk node refs)
       refs)))
 
 
-(define scan-refs-walk
+(define scan-refs-walk :effects []
   (fn (node (refs :as list))
     (cond
       ;; Symbol starting with ~ → component reference
@@ -67,7 +67,7 @@
 ;; Given a component name and an environment, compute all components
 ;; that it can transitively render.  Handles cycles via seen-set.
 
-(define transitive-deps-walk
+(define transitive-deps-walk :effects []
   (fn ((n :as string) (seen :as list) (env :as dict))
     (when (not (contains? seen n))
       (append! seen n)
@@ -82,7 +82,7 @@
           :else nil)))))
 
 
-(define transitive-deps
+(define transitive-deps :effects []
   (fn ((name :as string) (env :as dict))
     (let ((seen (list))
           (key (if (starts-with? name "~") name (str "~" name))))
@@ -100,7 +100,7 @@
 ;;   (env-components env) → list of component names in env
 ;;   (component-set-deps! comp deps) → store deps on component
 
-(define compute-all-deps
+(define compute-all-deps :effects [mutation]
   (fn ((env :as dict))
     (for-each
       (fn ((name :as string))
@@ -119,7 +119,7 @@
 ;; Platform interface:
 ;;   (regex-find-all pattern source) → list of matched group strings
 
-(define scan-components-from-source
+(define scan-components-from-source :effects []
   (fn ((source :as string))
     (let ((matches (regex-find-all "\\(~([a-zA-Z_][a-zA-Z0-9_\\-]*)" source)))
       (map (fn ((m :as string)) (str "~" m)) matches))))
@@ -131,7 +131,7 @@
 ;; Scans page source for direct component references, then computes
 ;; the transitive closure.  Returns list of ~names.
 
-(define components-needed
+(define components-needed :effects []
   (fn ((page-source :as string) (env :as dict))
     (let ((direct (scan-components-from-source page-source))
           (all-needed (list)))
@@ -165,7 +165,7 @@
 ;;
 ;; This replaces the "send everything" approach with per-page bundles.
 
-(define page-component-bundle
+(define page-component-bundle :effects []
   (fn ((page-source :as string) (env :as dict))
     (components-needed page-source env)))
 
@@ -180,7 +180,7 @@
 ;;   (component-css-classes c) → set/list of class strings
 ;;   (scan-css-classes source) → set/list of class strings from source
 
-(define page-css-classes
+(define page-css-classes :effects []
   (fn ((page-source :as string) (env :as dict))
     (let ((needed (components-needed page-source env))
           (classes (list)))
@@ -218,7 +218,7 @@
 ;;   (component-io-refs c)        → cached IO ref list (may be empty)
 ;;   (component-set-io-refs! c r) → cache IO refs on component
 
-(define scan-io-refs-walk
+(define scan-io-refs-walk :effects []
   (fn (node (io-names :as list) (refs :as list))
     (cond
       ;; Symbol → check if name is in the IO set
@@ -241,7 +241,7 @@
       :else nil)))
 
 
-(define scan-io-refs
+(define scan-io-refs :effects []
   (fn (node (io-names :as list))
     (let ((refs (list)))
       (scan-io-refs-walk node io-names refs)
@@ -252,7 +252,7 @@
 ;; 9. Transitive IO refs — follow component deps and union IO refs
 ;; --------------------------------------------------------------------------
 
-(define transitive-io-refs-walk
+(define transitive-io-refs-walk :effects []
   (fn ((n :as string) (seen :as list) (all-refs :as list) (env :as dict) (io-names :as list))
     (when (not (contains? seen n))
       (append! seen n)
@@ -285,7 +285,7 @@
           :else nil)))))
 
 
-(define transitive-io-refs
+(define transitive-io-refs :effects []
   (fn ((name :as string) (env :as dict) (io-names :as list))
     (let ((all-refs (list))
           (seen (list))
@@ -298,7 +298,7 @@
 ;; 10. Compute IO refs for all components in an environment
 ;; --------------------------------------------------------------------------
 
-(define compute-all-io-refs
+(define compute-all-io-refs :effects [mutation]
   (fn ((env :as dict) (io-names :as list))
     (for-each
       (fn ((name :as string))
@@ -308,7 +308,7 @@
       (env-components env))))
 
 
-(define component-io-refs-cached
+(define component-io-refs-cached :effects []
   (fn ((name :as string) (env :as dict) (io-names :as list))
     (let ((key (if (starts-with? name "~") name (str "~" name))))
       (let ((val (env-get env key)))
@@ -319,7 +319,7 @@
           ;; Fallback: not yet cached (shouldn't happen after compute-all-io-refs)
           (transitive-io-refs name env io-names))))))
 
-(define component-pure?
+(define component-pure? :effects []
   (fn ((name :as string) (env :as dict) (io-names :as list))
     (let ((key (if (starts-with? name "~") name (str "~" name))))
       (let ((val (env-get env key)))
@@ -343,7 +343,7 @@
 ;;
 ;; Returns: "server" | "client"
 
-(define render-target
+(define render-target :effects []
   (fn ((name :as string) (env :as dict) (io-names :as list))
     (let ((key (if (starts-with? name "~") name (str "~" name))))
       (let ((val (env-get env key)))
@@ -372,7 +372,7 @@
 ;; The async evaluator and client router both use it to make decisions
 ;; without recomputing at every request.
 
-(define page-render-plan
+(define page-render-plan :effects []
   (fn ((page-source :as string) (env :as dict) (io-names :as list))
     (let ((needed (components-needed page-source env))
           (comp-targets (dict))
@@ -450,7 +450,7 @@
 ;; --------------------------------------------------------------------------
 ;; Moved from platform to spec: pure logic using type predicates.
 
-(define env-components
+(define env-components :effects []
   (fn ((env :as dict))
     (filter
       (fn ((k :as string))
diff --git a/shared/sx/ref/engine.sx b/shared/sx/ref/engine.sx
index 9f1d9e9..e070536 100644
--- a/shared/sx/ref/engine.sx
+++ b/shared/sx/ref/engine.sx
@@ -31,7 +31,7 @@
 ;; Parses the sx-trigger attribute value into a list of trigger descriptors.
 ;; Each descriptor is a dict with "event" and "modifiers" keys.
 
-(define parse-time
+(define parse-time :effects []
   (fn ((s :as string))
     ;; Parse time string: "2s" → 2000, "500ms" → 500
     ;; Uses nested if (not cond) because cond misclassifies 2-element
@@ -42,7 +42,7 @@
           (parse-int s 0))))))
 
 
-(define parse-trigger-spec
+(define parse-trigger-spec :effects []
   (fn ((spec :as string))
     ;; Parse "click delay:500ms once,change" → list of trigger descriptors
     (if (nil? spec)
@@ -80,7 +80,7 @@
             raw-parts))))))
 
 
-(define default-trigger
+(define default-trigger :effects []
   (fn ((tag-name :as string))
     ;; Default trigger for element type
     (cond
@@ -98,7 +98,7 @@
 ;; Verb extraction
 ;; --------------------------------------------------------------------------
 
-(define get-verb-info
+(define get-verb-info :effects [io]
   (fn (el)
     ;; Check element for sx-get, sx-post, etc. Returns (dict "method" "url") or nil.
     (some
@@ -114,7 +114,7 @@
 ;; Request header building
 ;; --------------------------------------------------------------------------
 
-(define build-request-headers
+(define build-request-headers :effects [io]
   (fn (el (loaded-components :as list) (css-hash :as string))
     ;; Build the SX request headers dict
     (let ((headers (dict
@@ -150,7 +150,7 @@
 ;; Response header processing
 ;; --------------------------------------------------------------------------
 
-(define process-response-headers
+(define process-response-headers :effects []
   (fn ((get-header :as lambda))
     ;; Extract all SX response header directives into a dict.
     ;; get-header is (fn (name) → string or nil).
@@ -174,7 +174,7 @@
 ;; Swap specification parsing
 ;; --------------------------------------------------------------------------
 
-(define parse-swap-spec
+(define parse-swap-spec :effects []
   (fn ((raw-swap :as string) (global-transitions? :as boolean))
     ;; Parse "innerHTML transition:true" → dict with style + transition flag
     (let ((parts (split (or raw-swap DEFAULT_SWAP) " "))
@@ -193,7 +193,7 @@
 ;; Retry logic
 ;; --------------------------------------------------------------------------
 
-(define parse-retry-spec
+(define parse-retry-spec :effects []
   (fn ((retry-attr :as string))
     ;; Parse "exponential:1000:30000" → spec dict or nil
     (if (nil? retry-attr)
@@ -205,7 +205,7 @@
           "cap-ms"    (parse-int (nth parts 2) 30000))))))
 
 
-(define next-retry-ms
+(define next-retry-ms :effects []
   (fn ((current-ms :as number) (cap-ms :as number))
     ;; Exponential backoff: double current, cap at max
     (min (* current-ms 2) cap-ms)))
@@ -215,7 +215,7 @@
 ;; Form parameter filtering
 ;; --------------------------------------------------------------------------
 
-(define filter-params
+(define filter-params :effects []
   (fn ((params-spec :as string) (all-params :as list))
     ;; Filter form parameters by sx-params spec.
     ;; all-params is a list of (key value) pairs.
@@ -239,7 +239,7 @@
 ;; Target resolution
 ;; --------------------------------------------------------------------------
 
-(define resolve-target
+(define resolve-target :effects [io]
   (fn (el)
     ;; Resolve the swap target for an element
     (let ((sel (dom-get-attr el "sx-target")))
@@ -253,7 +253,7 @@
 ;; Optimistic updates
 ;; --------------------------------------------------------------------------
 
-(define apply-optimistic
+(define apply-optimistic :effects [mutation io]
   (fn (el)
     ;; Apply optimistic update preview. Returns state for reverting, or nil.
     (let ((directive (dom-get-attr el "sx-optimistic")))
@@ -278,7 +278,7 @@
           state)))))
 
 
-(define revert-optimistic
+(define revert-optimistic :effects [mutation io]
   (fn ((state :as dict))
     ;; Revert an optimistic update
     (when state
@@ -299,7 +299,7 @@
 ;; Out-of-band swap identification
 ;; --------------------------------------------------------------------------
 
-(define find-oob-swaps
+(define find-oob-swaps :effects [mutation io]
   (fn (container)
     ;; Find elements marked for out-of-band swapping.
     ;; Returns list of (dict "element" el "swap-type" type "target-id" id).
@@ -329,7 +329,7 @@
 ;; preserving event listeners, focus, scroll position, and form state
 ;; on keyed (id) elements.
 
-(define morph-node
+(define morph-node :effects [mutation io]
   (fn (old-node new-node)
     ;; Morph old-node to match new-node, preserving listeners/state.
     (cond
@@ -371,7 +371,7 @@
             (morph-children old-node new-node))))))
 
 
-(define sync-attrs
+(define sync-attrs :effects [mutation io]
   (fn (old-el new-el)
     ;; Sync attributes from new to old, but skip reactively managed attrs.
     ;; data-sx-reactive-attrs="style,class" means those attrs are owned by
@@ -398,7 +398,7 @@
         (dom-attr-list old-el)))))
 
 
-(define morph-children
+(define morph-children :effects [mutation io]
   (fn (old-parent new-parent)
     ;; Reconcile children of old-parent to match new-parent.
     ;; Keyed elements (with id) are matched and moved in-place.
@@ -472,7 +472,7 @@
 ;;   - Lakes = server substance (content, morphed)
 ;;   - The morph = Aufhebung (cancellation/preservation/elevation of both)
 
-(define morph-island-children
+(define morph-island-children :effects [mutation io]
   (fn (old-island new-island)
     ;; Find all lake and marsh slots in both old and new islands
     (let ((old-lakes (dom-query-all old-island "[data-sx-lake]"))
@@ -522,7 +522,7 @@
 ;; as SX and rendered in the island's signal context. If the marsh has a
 ;; :transform function, it reshapes the content before evaluation.
 
-(define morph-marsh
+(define morph-marsh :effects [mutation io]
   (fn (old-marsh new-marsh island-el)
     (let ((transform (dom-get-data old-marsh "sx-marsh-transform"))
           (env (dom-get-data old-marsh "sx-marsh-env"))
@@ -555,7 +555,7 @@
 ;;
 ;; Values are JSON-parsed: "7" → 7, "\"hello\"" → "hello", "true" → true.
 
-(define process-signal-updates
+(define process-signal-updates :effects [mutation io]
   (fn (root)
     (let ((signal-els (dom-query-all root "[data-sx-signal]")))
       (for-each
@@ -576,7 +576,7 @@
 ;; Swap dispatch
 ;; --------------------------------------------------------------------------
 
-(define swap-dom-nodes
+(define swap-dom-nodes :effects [mutation io]
   (fn (target new-nodes (strategy :as string))
     ;; Execute a swap strategy on live DOM nodes.
     ;; new-nodes is typically a DocumentFragment or Element.
@@ -630,7 +630,7 @@
             (morph-children target wrapper))))))
 
 
-(define insert-remaining-siblings
+(define insert-remaining-siblings :effects [mutation io]
   (fn (parent ref-node sib)
     ;; Insert sibling chain after ref-node
     (when sib
@@ -643,7 +643,7 @@
 ;; String-based swap (fallback for HTML responses)
 ;; --------------------------------------------------------------------------
 
-(define swap-html-string
+(define swap-html-string :effects [mutation io]
   (fn (target (html :as string) (strategy :as string))
     ;; Execute a swap strategy using an HTML string (DOMParser pipeline).
     (case strategy
@@ -674,7 +674,7 @@
 ;; History management
 ;; --------------------------------------------------------------------------
 
-(define handle-history
+(define handle-history :effects [io]
   (fn (el (url :as string) (resp-headers :as dict))
     ;; Process history push/replace based on element attrs and response headers
     (let ((push-url     (dom-get-attr el "sx-push-url"))
@@ -700,7 +700,7 @@
 
 (define PRELOAD_TTL 30000)  ;; 30 seconds
 
-(define preload-cache-get
+(define preload-cache-get :effects [mutation]
   (fn ((cache :as dict) (url :as string))
     ;; Get and consume a cached preload response.
     ;; Returns (dict "text" ... "content-type" ...) or nil.
@@ -712,7 +712,7 @@
           (do (dict-delete! cache url) entry))))))
 
 
-(define preload-cache-set
+(define preload-cache-set :effects [mutation]
   (fn ((cache :as dict) (url :as string) (text :as string) (content-type :as string))
     ;; Store a preloaded response
     (dict-set! cache url
@@ -725,7 +725,7 @@
 ;; Maps trigger event names to binding strategies.
 ;; This is the logic; actual browser event binding is platform interface.
 
-(define classify-trigger
+(define classify-trigger :effects []
   (fn ((trigger :as dict))
     ;; Classify a parsed trigger descriptor for binding.
     ;; Returns one of: "poll", "intersect", "load", "revealed", "event"
@@ -742,7 +742,7 @@
 ;; Boost logic
 ;; --------------------------------------------------------------------------
 
-(define should-boost-link?
+(define should-boost-link? :effects [io]
   (fn (link)
     ;; Whether a link inside an sx-boost container should be boosted
     (let ((href (dom-get-attr link "href")))
@@ -756,7 +756,7 @@
            (not (dom-has-attr? link "sx-disable"))))))
 
 
-(define should-boost-form?
+(define should-boost-form? :effects [io]
   (fn (form)
     ;; Whether a form inside an sx-boost container should be boosted
     (and (not (dom-has-attr? form "sx-get"))
@@ -768,7 +768,7 @@
 ;; SSE event classification
 ;; --------------------------------------------------------------------------
 
-(define parse-sse-swap
+(define parse-sse-swap :effects [io]
   (fn (el)
     ;; Parse sx-sse-swap attribute
     ;; Returns event name to listen for (default "message")
diff --git a/shared/sx/ref/eval.sx b/shared/sx/ref/eval.sx
index 8cad009..09467f6 100644
--- a/shared/sx/ref/eval.sx
+++ b/shared/sx/ref/eval.sx
@@ -55,7 +55,7 @@
 ;; --------------------------------------------------------------------------
 
 (define trampoline
-  (fn (val)
+  (fn ((val :as any))
     ;; Iteratively resolve thunks until we get an actual value.
     ;; Each target implements thunk? and thunk-expr/thunk-env.
     (let ((result val))
@@ -151,6 +151,8 @@
               (= name "defpage")     (sf-defpage args env)
               (= name "defquery")    (sf-defquery args env)
               (= name "defaction")   (sf-defaction args env)
+              (= name "deftype")     (sf-deftype args env)
+              (= name "defeffect")   (sf-defeffect args env)
               (= name "begin")       (sf-begin args env)
               (= name "do")          (sf-begin args env)
               (= name "quote")       (sf-quote args env)
@@ -506,11 +508,32 @@
 
 (define sf-define
   (fn ((args :as list) (env :as dict))
+    ;; Detect :effects keyword: (define name :effects [...] value)
     (let ((name-sym (first args))
-          (value    (trampoline (eval-expr (nth args 1) env))))
+          (has-effects (and (>= (len args) 4)
+                           (= (type-of (nth args 1)) "keyword")
+                           (= (keyword-name (nth args 1)) "effects")))
+          (val-idx (if (and (>= (len args) 4)
+                            (= (type-of (nth args 1)) "keyword")
+                            (= (keyword-name (nth args 1)) "effects"))
+                     3 1))
+          (value (trampoline (eval-expr (nth args val-idx) env))))
       (when (and (lambda? value) (nil? (lambda-name value)))
         (set-lambda-name! value (symbol-name name-sym)))
       (env-set! env (symbol-name name-sym) value)
+      ;; Store effect annotation if declared
+      (when has-effects
+        (let ((effects-raw (nth args 2))
+              (effect-list (if (= (type-of effects-raw) "list")
+                             (map (fn (e) (if (= (type-of e) "symbol")
+                                            (symbol-name e) (str e)))
+                                  effects-raw)
+                             (list (str effects-raw))))
+              (effect-anns (if (env-has? env "*effect-annotations*")
+                             (env-get env "*effect-annotations*")
+                             (dict))))
+          (dict-set! effect-anns (symbol-name name-sym) effect-list)
+          (env-set! env "*effect-annotations*" effect-anns)))
       value)))
 
 
@@ -528,11 +551,24 @@
           (has-children (nth parsed 1))
           (param-types (nth parsed 2))
           (affinity   (defcomp-kwarg args "affinity" "auto")))
-      (let ((comp (make-component comp-name params has-children body env affinity)))
+      (let ((comp (make-component comp-name params has-children body env affinity))
+            (effects (defcomp-kwarg args "effects" nil)))
         ;; Store type annotations if any were declared
         (when (and (not (nil? param-types))
                    (not (empty? (keys param-types))))
           (component-set-param-types! comp param-types))
+        ;; Store effect annotation if declared
+        (when (not (nil? effects))
+          (let ((effect-list (if (= (type-of effects) "list")
+                               (map (fn (e) (if (= (type-of e) "symbol")
+                                              (symbol-name e) (str e)))
+                                    effects)
+                               (list (str effects))))
+                (effect-anns (if (env-has? env "*effect-annotations*")
+                               (env-get env "*effect-annotations*")
+                               (dict))))
+            (dict-set! effect-anns (symbol-name name-sym) effect-list)
+            (env-set! env "*effect-annotations*" effect-anns)))
         (env-set! env (symbol-name name-sym) comp)
         comp))))
 
@@ -654,6 +690,82 @@
       value)))
 
 
+;; -- deftype helpers (must be in eval.sx, not types.sx, because
+;;    sf-deftype is always compiled but types.sx is a spec module) --
+
+(define make-type-def
+  (fn ((name :as string) (params :as list) body)
+    {:name name :params params :body body}))
+
+(define normalize-type-body
+  (fn (body)
+    ;; Convert AST type expressions to type representation.
+    ;; Symbols → strings, (union ...) → (or ...), dict keys → strings.
+    (cond
+      (nil? body) "nil"
+      (= (type-of body) "symbol")
+        (symbol-name body)
+      (= (type-of body) "string")
+        body
+      (= (type-of body) "keyword")
+        (keyword-name body)
+      (= (type-of body) "dict")
+        ;; Record type — normalize values
+        (map-dict (fn (k v) (normalize-type-body v)) body)
+      (= (type-of body) "list")
+        (if (empty? body) "any"
+          (let ((head (first body)))
+            (let ((head-name (if (= (type-of head) "symbol")
+                               (symbol-name head) (str head))))
+              ;; (union a b) → (or a b)
+              (if (= head-name "union")
+                (cons "or" (map normalize-type-body (rest body)))
+                ;; (or a b), (list-of t), (-> ...) etc.
+                (cons head-name (map normalize-type-body (rest body)))))))
+      :else (str body))))
+
+(define sf-deftype
+  (fn ((args :as list) (env :as dict))
+    ;; (deftype name body) or (deftype (name a b ...) body)
+    (let ((name-or-form (first args))
+          (body-expr (nth args 1))
+          (type-name nil)
+          (type-params (list)))
+      ;; Parse name — symbol or (symbol params...)
+      (if (= (type-of name-or-form) "symbol")
+        (set! type-name (symbol-name name-or-form))
+        (when (= (type-of name-or-form) "list")
+          (set! type-name (symbol-name (first name-or-form)))
+          (set! type-params
+            (map (fn (p) (if (= (type-of p) "symbol")
+                           (symbol-name p) (str p)))
+                 (rest name-or-form)))))
+      ;; Normalize and store in *type-registry*
+      (let ((body (normalize-type-body body-expr))
+            (registry (if (env-has? env "*type-registry*")
+                        (env-get env "*type-registry*")
+                        (dict))))
+        (dict-set! registry type-name
+          (make-type-def type-name type-params body))
+        (env-set! env "*type-registry*" registry)
+        nil))))
+
+
+(define sf-defeffect
+  (fn ((args :as list) (env :as dict))
+    ;; (defeffect name) — register an effect name
+    (let ((effect-name (if (= (type-of (first args)) "symbol")
+                         (symbol-name (first args))
+                         (str (first args))))
+          (registry (if (env-has? env "*effect-registry*")
+                      (env-get env "*effect-registry*")
+                      (list))))
+      (when (not (contains? registry effect-name))
+        (append! registry effect-name))
+      (env-set! env "*effect-registry*" registry)
+      nil)))
+
+
 (define sf-begin
   (fn ((args :as list) (env :as dict))
     (if (empty? args)
diff --git a/shared/sx/ref/js.sx b/shared/sx/ref/js.sx
index 8de1cb5..6dfc6df 100644
--- a/shared/sx/ref/js.sx
+++ b/shared/sx/ref/js.sx
@@ -1318,10 +1318,15 @@
 
 (define js-emit-define
   (fn (expr)
+    ;; Handle (define name :effects [...] value) — skip :effects annotation
     (let ((name (if (= (type-of (nth expr 1)) "symbol")
                   (symbol-name (nth expr 1))
                   (str (nth expr 1))))
-          (val-expr (nth expr 2)))
+          (val-expr (if (and (>= (len expr) 5)
+                             (= (type-of (nth expr 2)) "keyword")
+                             (= (keyword-name (nth expr 2)) "effects"))
+                      (nth expr 4)
+                      (nth expr 2))))
       (if (nil? val-expr)
         (str "var " (js-mangle name) " = NIL;")
         ;; Detect zero-arg self-tail-recursive functions → while loops
diff --git a/shared/sx/ref/orchestration.sx b/shared/sx/ref/orchestration.sx
index 9ee6e56..2fd1f94 100644
--- a/shared/sx/ref/orchestration.sx
+++ b/shared/sx/ref/orchestration.sx
@@ -33,7 +33,7 @@
 ;; Event dispatch helpers
 ;; --------------------------------------------------------------------------
 
-(define dispatch-trigger-events
+(define dispatch-trigger-events :effects [mutation io]
   (fn (el (header-val :as string))
     ;; Dispatch events from SX-Trigger / SX-Trigger-After-Swap headers.
     ;; Value can be JSON object (name → detail) or comma-separated names.
@@ -58,7 +58,7 @@
 ;; CSS tracking
 ;; --------------------------------------------------------------------------
 
-(define init-css-tracking
+(define init-css-tracking :effects [mutation io]
   (fn ()
     ;; Read initial CSS hash from meta tag
     (let ((meta (dom-query "meta[name=\"sx-css-classes\"]")))
@@ -72,7 +72,7 @@
 ;; Request execution
 ;; --------------------------------------------------------------------------
 
-(define execute-request
+(define execute-request :effects [mutation io]
   (fn (el (verbInfo :as dict) (extraParams :as dict))
     ;; Gate checks then delegate to do-fetch.
     ;; verbInfo: dict with "method" and "url" (or nil to read from element).
@@ -105,7 +105,7 @@
                         extraParams))))))))))))
 
 
-(define do-fetch
+(define do-fetch :effects [mutation io]
   (fn (el (verb :as string) (method :as string) (url :as string) (extraParams :as dict))
     ;; Execute the actual fetch. Manages abort, headers, body, loading state.
     (let ((sync (dom-get-attr el "sx-sync")))
@@ -201,7 +201,7 @@
                       (dict "error" err))))))))))))
 
 
-(define handle-fetch-success
+(define handle-fetch-success :effects [mutation io]
   (fn (el (url :as string) (verb :as string) (extraParams :as dict) get-header (text :as string))
     ;; Route a successful response through the appropriate handler.
     (let ((resp-headers (process-response-headers get-header)))
@@ -269,7 +269,7 @@
               (dict "target" target-el "swap" swap-style)))))))
 
 
-(define handle-sx-response
+(define handle-sx-response :effects [mutation io]
   (fn (el target (text :as string) (swap-style :as string) (use-transition :as boolean))
     ;; Handle SX-format response: strip components, extract CSS, render, swap.
     (let ((cleaned (strip-component-scripts text)))
@@ -300,7 +300,7 @@
                     (post-swap target)))))))))))
 
 
-(define handle-html-response
+(define handle-html-response :effects [mutation io]
   (fn (el target (text :as string) (swap-style :as string) (use-transition :as boolean))
     ;; Handle HTML-format response: parse, OOB, select, swap.
     (let ((doc (dom-parse-html-document text)))
@@ -337,7 +337,7 @@
 ;; Retry
 ;; --------------------------------------------------------------------------
 
-(define handle-retry
+(define handle-retry :effects [mutation io]
   (fn (el (verb :as string) (method :as string) (url :as string) (extraParams :as dict))
     ;; Handle retry on failure if sx-retry is configured
     (let ((retry-attr (dom-get-attr el "sx-retry"))
@@ -357,7 +357,7 @@
 ;; Trigger binding
 ;; --------------------------------------------------------------------------
 
-(define bind-triggers
+(define bind-triggers :effects [mutation io]
   (fn (el (verbInfo :as dict))
     ;; Bind triggers from sx-trigger attribute (or defaults)
     (let ((triggers (or (parse-trigger-spec (dom-get-attr el "sx-trigger"))
@@ -392,7 +392,7 @@
         triggers))))
 
 
-(define bind-event
+(define bind-event :effects [mutation io]
   (fn (el (event-name :as string) (mods :as dict) (verbInfo :as dict))
     ;; Bind a standard DOM event trigger.
     ;; Handles delay, once, changed, optimistic, preventDefault.
@@ -453,7 +453,7 @@
 ;; Post-swap lifecycle
 ;; --------------------------------------------------------------------------
 
-(define post-swap
+(define post-swap :effects [mutation io]
   (fn (root)
     ;; Run lifecycle after swap: activate scripts, process SX, hydrate, process
     (activate-scripts root)
@@ -474,7 +474,7 @@
 ;;
 ;; Example: (button :sx-get "/search" :sx-on-settle "(reset! (use-store \"count\") 0)")
 
-(define process-settle-hooks
+(define process-settle-hooks :effects [mutation io]
   (fn (el)
     (let ((settle-expr (dom-get-attr el "sx-on-settle")))
       (when (and settle-expr (not (empty? settle-expr)))
@@ -484,7 +484,7 @@
             exprs))))))
 
 
-(define activate-scripts
+(define activate-scripts :effects [mutation io]
   (fn (root)
     ;; Re-activate scripts in swapped content.
     ;; Scripts inserted via innerHTML are inert — clone to make them execute.
@@ -505,7 +505,7 @@
 ;; OOB swap processing
 ;; --------------------------------------------------------------------------
 
-(define process-oob-swaps
+(define process-oob-swaps :effects [mutation io]
   (fn (container (swap-fn :as lambda))
     ;; Find and process out-of-band swaps in container.
     ;; swap-fn is (fn (target oob-element swap-type) ...).
@@ -529,7 +529,7 @@
 ;; Head element hoisting
 ;; --------------------------------------------------------------------------
 
-(define hoist-head-elements
+(define hoist-head-elements :effects [mutation io]
   (fn (container)
     ;; Move style[data-sx-css] and link[rel=stylesheet] to <head>
     ;; so they take effect globally.
@@ -551,7 +551,7 @@
 ;; Boost processing
 ;; --------------------------------------------------------------------------
 
-(define process-boosted
+(define process-boosted :effects [mutation io]
   (fn (root)
     ;; Find [sx-boost] containers and boost their descendants
     (for-each
@@ -560,7 +560,7 @@
       (dom-query-all (or root (dom-body)) "[sx-boost]"))))
 
 
-(define boost-descendants
+(define boost-descendants :effects [mutation io]
   (fn (container)
     ;; Boost links and forms within a container.
     ;; The sx-boost attribute value is the default target selector
@@ -609,7 +609,7 @@
 (define _page-data-cache (dict))
 (define _page-data-cache-ttl 30000)  ;; 30 seconds in ms
 
-(define page-data-cache-key
+(define page-data-cache-key :effects []
   (fn ((page-name :as string) (params :as dict))
     ;; Build a cache key from page name + params.
     ;; Params are from route matching so order is deterministic.
@@ -623,7 +623,7 @@
             (keys params))
           (str base ":" (join "&" parts)))))))
 
-(define page-data-cache-get
+(define page-data-cache-get :effects [mutation io]
   (fn ((cache-key :as string))
     ;; Return cached data if fresh, else nil.
     (let ((entry (get _page-data-cache cache-key)))
@@ -635,7 +635,7 @@
             nil)
           (get entry "data"))))))
 
-(define page-data-cache-set
+(define page-data-cache-set :effects [mutation io]
   (fn ((cache-key :as string) data)
     ;; Store data with current timestamp.
     (dict-set! _page-data-cache cache-key
@@ -646,7 +646,7 @@
 ;; Client-side routing — cache management
 ;; --------------------------------------------------------------------------
 
-(define invalidate-page-cache
+(define invalidate-page-cache :effects [mutation io]
   (fn ((page-name :as string))
     ;; Clear cached data for a page. Removes all cache entries whose key
     ;; matches page-name (exact) or starts with "page-name:" (with params).
@@ -659,14 +659,14 @@
     (sw-post-message {"type" "invalidate" "page" page-name})
     (log-info (str "sx:cache invalidate " page-name))))
 
-(define invalidate-all-page-cache
+(define invalidate-all-page-cache :effects [mutation io]
   (fn ()
     ;; Clear all cached page data and notify service worker.
     (set! _page-data-cache (dict))
     (sw-post-message {"type" "invalidate" "page" "*"})
     (log-info "sx:cache invalidate *")))
 
-(define update-page-cache
+(define update-page-cache :effects [mutation io]
   (fn ((page-name :as string) data)
     ;; Replace cached data for a page with server-provided data.
     ;; Uses a bare page-name key (no params) — the server knows the
@@ -675,7 +675,7 @@
       (page-data-cache-set cache-key data)
       (log-info (str "sx:cache update " page-name)))))
 
-(define process-cache-directives
+(define process-cache-directives :effects [mutation io]
   (fn (el (resp-headers :as dict) (response-text :as string))
     ;; Process cache invalidation and update directives from both
     ;; element attributes and response headers.
@@ -721,7 +721,7 @@
 
 (define _optimistic-snapshots (dict))
 
-(define optimistic-cache-update
+(define optimistic-cache-update :effects [mutation]
   (fn ((cache-key :as string) (mutator :as lambda))
     ;; Apply predicted mutation to cached data. Saves snapshot for rollback.
     ;; Returns predicted data or nil if no cached data exists.
@@ -734,7 +734,7 @@
           (page-data-cache-set cache-key predicted)
           predicted)))))
 
-(define optimistic-cache-revert
+(define optimistic-cache-revert :effects [mutation]
   (fn ((cache-key :as string))
     ;; Revert to pre-mutation snapshot. Returns restored data or nil.
     (let ((snapshot (get _optimistic-snapshots cache-key)))
@@ -743,12 +743,12 @@
         (dict-delete! _optimistic-snapshots cache-key)
         snapshot))))
 
-(define optimistic-cache-confirm
+(define optimistic-cache-confirm :effects [mutation]
   (fn ((cache-key :as string))
     ;; Server accepted — discard the rollback snapshot.
     (dict-delete! _optimistic-snapshots cache-key)))
 
-(define submit-mutation
+(define submit-mutation :effects [mutation io]
   (fn ((page-name :as string) (params :as dict) (action-name :as string) payload (mutator-fn :as lambda) (on-complete :as lambda))
     ;; Optimistic mutation: predict locally, send to server, confirm or revert.
     ;; on-complete is called with "confirmed" or "reverted" status.
@@ -787,14 +787,14 @@
 (define _is-online true)
 (define _offline-queue (list))
 
-(define offline-is-online?
+(define offline-is-online? :effects [io]
   (fn () _is-online))
 
-(define offline-set-online!
+(define offline-set-online! :effects [mutation]
   (fn ((val :as boolean))
     (set! _is-online val)))
 
-(define offline-queue-mutation
+(define offline-queue-mutation :effects [mutation io]
   (fn ((action-name :as string) payload (page-name :as string) (params :as dict) (mutator-fn :as lambda))
     ;; Queue a mutation for later sync. Apply optimistic update locally.
     (let ((cache-key (page-data-cache-key page-name params))
@@ -813,7 +813,7 @@
       (log-info (str "sx:offline queued " action-name " (" (len _offline-queue) " pending)"))
       entry)))
 
-(define offline-sync
+(define offline-sync :effects [mutation io]
   (fn ()
     ;; Replay all pending mutations. Called on reconnect.
     (let ((pending (filter (fn ((e :as dict)) (= (get e "status") "pending")) _offline-queue)))
@@ -830,11 +830,11 @@
                 (log-warn (str "sx:offline sync failed " (get entry "action") ": " error)))))
           pending)))))
 
-(define offline-pending-count
+(define offline-pending-count :effects [io]
   (fn ()
     (len (filter (fn ((e :as dict)) (= (get e "status") "pending")) _offline-queue))))
 
-(define offline-aware-mutation
+(define offline-aware-mutation :effects [mutation io]
   (fn ((page-name :as string) (params :as dict) (action-name :as string) payload (mutator-fn :as lambda) (on-complete :as lambda))
     ;; Top-level mutation function. Routes to submit-mutation when online,
     ;; offline-queue-mutation when offline.
@@ -849,7 +849,7 @@
 ;; Client-side routing
 ;; --------------------------------------------------------------------------
 
-(define current-page-layout
+(define current-page-layout :effects [io]
   (fn ()
     ;; Find the layout name of the currently displayed page by matching
     ;; the browser URL against the page route table.
@@ -859,7 +859,7 @@
         (or (get match "layout") "")))))
 
 
-(define swap-rendered-content
+(define swap-rendered-content :effects [mutation io]
   (fn (target rendered (pathname :as string))
     ;; Swap rendered DOM content into target and run post-processing.
     ;; Shared by pure and data page client routes.
@@ -875,7 +875,7 @@
       (log-info (str "sx:route client " pathname)))))
 
 
-(define resolve-route-target
+(define resolve-route-target :effects [io]
   (fn ((target-sel :as string))
     ;; Resolve a target selector to a DOM element, or nil.
     (if (and target-sel (not (= target-sel "true")))
@@ -883,7 +883,7 @@
       nil)))
 
 
-(define deps-satisfied?
+(define deps-satisfied? :effects [io]
   (fn ((match :as dict))
     ;; Check if all component deps for a page are loaded client-side.
     (let ((deps (get match "deps"))
@@ -893,7 +893,7 @@
         (every? (fn ((dep :as string)) (contains? loaded dep)) deps)))))
 
 
-(define try-client-route
+(define try-client-route :effects [mutation io]
   (fn ((pathname :as string) (target-sel :as string))
     ;; Try to render a page client-side. Returns true if successful, false otherwise.
     ;; target-sel is the CSS selector for the swap target (from sx-boost value).
@@ -1011,7 +1011,7 @@
                               true))))))))))))))))))
 
 
-(define bind-client-route-link
+(define bind-client-route-link :effects [mutation io]
   (fn (link (href :as string))
     ;; Bind a boost link with client-side routing. If the route can be
     ;; rendered client-side (pure page, no :data), do so. Otherwise
@@ -1026,7 +1026,7 @@
 ;; SSE processing
 ;; --------------------------------------------------------------------------
 
-(define process-sse
+(define process-sse :effects [mutation io]
   (fn (root)
     ;; Find and bind SSE elements
     (for-each
@@ -1037,7 +1037,7 @@
       (dom-query-all (or root (dom-body)) "[sx-sse]"))))
 
 
-(define bind-sse
+(define bind-sse :effects [mutation io]
   (fn (el)
     ;; Connect to SSE endpoint and bind swap handler
     (let ((url (dom-get-attr el "sx-sse")))
@@ -1049,7 +1049,7 @@
               (bind-sse-swap el data))))))))
 
 
-(define bind-sse-swap
+(define bind-sse-swap :effects [mutation io]
   (fn (el (data :as string))
     ;; Handle an SSE event: swap data into element
     (let ((target (resolve-target el))
@@ -1081,7 +1081,7 @@
 ;; Inline event handlers
 ;; --------------------------------------------------------------------------
 
-(define bind-inline-handlers
+(define bind-inline-handlers :effects [mutation io]
   (fn (root)
     ;; Find elements with sx-on:* attributes and bind SX event handlers.
     ;; Handler bodies are SX expressions evaluated with `event` and `this`
@@ -1115,7 +1115,7 @@
 ;; Preload
 ;; --------------------------------------------------------------------------
 
-(define bind-preload-for
+(define bind-preload-for :effects [mutation io]
   (fn (el)
     ;; Bind preload event listeners based on sx-preload attribute
     (let ((preload-attr (dom-get-attr el "sx-preload")))
@@ -1134,7 +1134,7 @@
                       (loaded-component-names) _css-hash)))))))))))
 
 
-(define do-preload
+(define do-preload :effects [mutation io]
   (fn ((url :as string) (headers :as dict))
     ;; Execute a preload fetch into the cache
     (when (nil? (preload-cache-get _preload-cache url))
@@ -1148,7 +1148,7 @@
 (define VERB_SELECTOR
   (str "[sx-get],[sx-post],[sx-put],[sx-delete],[sx-patch]"))
 
-(define process-elements
+(define process-elements :effects [mutation io]
   (fn (root)
     ;; Find all elements with sx-* verb attributes and process them.
     (let ((els (dom-query-all (or root (dom-body)) VERB_SELECTOR)))
@@ -1165,7 +1165,7 @@
     (process-emit-elements root)))
 
 
-(define process-one
+(define process-one :effects [mutation io]
   (fn (el)
     ;; Process a single element with an sx-* verb attribute
     (let ((verb-info (get-verb-info el)))
@@ -1193,7 +1193,7 @@
 ;; On click → dispatches CustomEvent "cart:add" with detail {id:42, name:"Widget"}
 ;; The event bubbles up to the island container where bridge-event catches it.
 
-(define process-emit-elements
+(define process-emit-elements :effects [mutation io]
   (fn (root)
     (let ((els (dom-query-all (or root (dom-body)) "[data-sx-emit]")))
       (for-each
@@ -1214,7 +1214,7 @@
 ;; History: popstate handler
 ;; --------------------------------------------------------------------------
 
-(define handle-popstate
+(define handle-popstate :effects [mutation io]
   (fn ((scrollY :as number))
     ;; Handle browser back/forward navigation.
     ;; Derive target from [sx-boost] container or fall back to #main-panel.
@@ -1241,7 +1241,7 @@
 ;; Initialization
 ;; --------------------------------------------------------------------------
 
-(define engine-init
+(define engine-init :effects [mutation io]
   (fn ()
     ;; Initialize: CSS tracking, scripts, hydrate, process.
     (do
diff --git a/shared/sx/ref/parser.sx b/shared/sx/ref/parser.sx
index f2e2943..919806b 100644
--- a/shared/sx/ref/parser.sx
+++ b/shared/sx/ref/parser.sx
@@ -49,20 +49,20 @@
 ;; --------------------------------------------------------------------------
 ;; Returns a list of top-level AST expressions.
 
-(define sx-parse
+(define sx-parse :effects []
   (fn ((source :as string))
     (let ((pos 0)
           (len-src (len source)))
 
       ;; -- Cursor helpers (closure over pos, source, len-src) --
 
-      (define skip-comment
+      (define skip-comment :effects []
         (fn ()
           (when (and (< pos len-src) (not (= (nth source pos) "\n")))
             (set! pos (inc pos))
             (skip-comment))))
 
-      (define skip-ws
+      (define skip-ws :effects []
         (fn ()
           (when (< pos len-src)
             (let ((ch (nth source pos)))
@@ -80,11 +80,11 @@
 
       ;; -- Atom readers --
 
-      (define read-string
+      (define read-string :effects []
         (fn ()
           (set! pos (inc pos))  ;; skip opening "
           (let ((buf ""))
-            (define read-str-loop
+            (define read-str-loop :effects []
               (fn ()
                 (if (>= pos len-src)
                   (error "Unterminated string")
@@ -110,10 +110,10 @@
             (read-str-loop)
             buf)))
 
-      (define read-ident
+      (define read-ident :effects []
         (fn ()
           (let ((start pos))
-            (define read-ident-loop
+            (define read-ident-loop :effects []
               (fn ()
                 (when (and (< pos len-src)
                            (ident-char? (nth source pos)))
@@ -122,19 +122,19 @@
             (read-ident-loop)
             (slice source start pos))))
 
-      (define read-keyword
+      (define read-keyword :effects []
         (fn ()
           (set! pos (inc pos))  ;; skip :
           (make-keyword (read-ident))))
 
-      (define read-number
+      (define read-number :effects []
         (fn ()
           (let ((start pos))
             ;; Optional leading minus
             (when (and (< pos len-src) (= (nth source pos) "-"))
               (set! pos (inc pos)))
             ;; Integer digits
-            (define read-digits
+            (define read-digits :effects []
               (fn ()
                 (when (and (< pos len-src)
                            (let ((c (nth source pos)))
@@ -158,7 +158,7 @@
               (read-digits))
             (parse-number (slice source start pos)))))
 
-      (define read-symbol
+      (define read-symbol :effects []
         (fn ()
           (let ((name (read-ident)))
             (cond
@@ -169,10 +169,10 @@
 
       ;; -- Composite readers --
 
-      (define read-list
+      (define read-list :effects []
         (fn ((close-ch :as string))
           (let ((items (list)))
-            (define read-list-loop
+            (define read-list-loop :effects []
               (fn ()
                 (skip-ws)
                 (if (>= pos len-src)
@@ -184,10 +184,10 @@
             (read-list-loop)
             items)))
 
-      (define read-map
+      (define read-map :effects []
         (fn ()
           (let ((result (dict)))
-            (define read-map-loop
+            (define read-map-loop :effects []
               (fn ()
                 (skip-ws)
                 (if (>= pos len-src)
@@ -206,10 +206,10 @@
 
       ;; -- Raw string reader (for #|...|) --
 
-      (define read-raw-string
+      (define read-raw-string :effects []
         (fn ()
           (let ((buf ""))
-            (define raw-loop
+            (define raw-loop :effects []
               (fn ()
                 (if (>= pos len-src)
                   (error "Unterminated raw string")
@@ -224,7 +224,7 @@
 
       ;; -- Main expression reader --
 
-      (define read-expr
+      (define read-expr :effects []
         (fn ()
           (skip-ws)
           (if (>= pos len-src)
@@ -322,7 +322,7 @@
 
       ;; -- Entry point: parse all top-level expressions --
       (let ((exprs (list)))
-        (define parse-loop
+        (define parse-loop :effects []
           (fn ()
             (skip-ws)
             (when (< pos len-src)
@@ -336,7 +336,7 @@
 ;; Serializer — AST → SX source text
 ;; --------------------------------------------------------------------------
 
-(define sx-serialize
+(define sx-serialize :effects []
   (fn (val)
     (case (type-of val)
       "nil"       "nil"
@@ -351,7 +351,7 @@
       :else       (str val))))
 
 
-(define sx-serialize-dict
+(define sx-serialize-dict :effects []
   (fn ((d :as dict))
     (str "{"
       (join " "
diff --git a/shared/sx/ref/platform_py.py b/shared/sx/ref/platform_py.py
index e2ccec0..e596a34 100644
--- a/shared/sx/ref/platform_py.py
+++ b/shared/sx/ref/platform_py.py
@@ -575,6 +575,11 @@ def strip_prefix(s, prefix):
     return s[len(prefix):] if s.startswith(prefix) else s
 
 
+def debug_log(*args):
+    import sys
+    print(*args, file=sys.stderr)
+
+
 def error(msg):
     raise EvalError(msg)
 
diff --git a/shared/sx/ref/render.sx b/shared/sx/ref/render.sx
index be53226..d97968f 100644
--- a/shared/sx/ref/render.sx
+++ b/shared/sx/ref/render.sx
@@ -71,13 +71,14 @@
 ;; Shared utilities
 ;; --------------------------------------------------------------------------
 
-(define definition-form?
+(define definition-form? :effects []
   (fn ((name :as string))
     (or (= name "define") (= name "defcomp") (= name "defisland")
-        (= name "defmacro") (= name "defstyle") (= name "defhandler"))))
+        (= name "defmacro") (= name "defstyle") (= name "defhandler")
+        (= name "deftype") (= name "defeffect"))))
 
 
-(define parse-element-args
+(define parse-element-args :effects [render]
   (fn ((args :as list) (env :as dict))
     ;; Parse (:key val :key2 val2 child1 child2) into (attrs-dict children-list)
     (let ((attrs (dict))
@@ -100,7 +101,7 @@
       (list attrs children))))
 
 
-(define render-attrs
+(define render-attrs :effects []
   (fn ((attrs :as dict))
     ;; Render an attrs dict to an HTML attribute string.
     ;; Used by adapter-html.sx and adapter-sx.sx.
@@ -132,13 +133,13 @@
 ;; eval-cond: find matching cond branch, return unevaluated body expr.
 ;; Handles both scheme-style ((test body) ...) and clojure-style
 ;; (test body test body ...).
-(define eval-cond
+(define eval-cond :effects []
   (fn ((clauses :as list) (env :as dict))
     (if (cond-scheme? clauses)
       (eval-cond-scheme clauses env)
       (eval-cond-clojure clauses env))))
 
-(define eval-cond-scheme
+(define eval-cond-scheme :effects []
   (fn ((clauses :as list) (env :as dict))
     (if (empty? clauses)
       nil
@@ -155,7 +156,7 @@
             body
             (eval-cond-scheme (rest clauses) env)))))))
 
-(define eval-cond-clojure
+(define eval-cond-clojure :effects []
   (fn ((clauses :as list) (env :as dict))
     (if (< (len clauses) 2)
       nil
@@ -172,7 +173,7 @@
 
 ;; process-bindings: evaluate let-binding pairs, return extended env.
 ;; bindings = ((name1 expr1) (name2 expr2) ...)
-(define process-bindings
+(define process-bindings :effects [mutation]
   (fn ((bindings :as list) (env :as dict))
     ;; env-extend (not merge) — Env is not a dict subclass, so merge()
     ;; returns an empty dict, losing all parent scope bindings.
@@ -194,7 +195,7 @@
 ;; Used by eval-list to dispatch rendering forms to the active adapter
 ;; (HTML, SX wire, or DOM) rather than evaluating them as function calls.
 
-(define is-render-expr?
+(define is-render-expr? :effects []
   (fn (expr)
     (if (or (not (= (type-of expr) "list")) (empty? expr))
       false
diff --git a/shared/sx/ref/router.sx b/shared/sx/ref/router.sx
index 266d65d..9eb8f1f 100644
--- a/shared/sx/ref/router.sx
+++ b/shared/sx/ref/router.sx
@@ -17,7 +17,7 @@
 ;; "/" → ()
 ;; "/docs/" → ("docs")
 
-(define split-path-segments
+(define split-path-segments :effects []
   (fn ((path :as string))
     (let ((trimmed (if (starts-with? path "/") (slice path 1) path)))
       (let ((trimmed2 (if (and (not (empty? trimmed))
@@ -35,7 +35,7 @@
 ;; "/docs/<slug>" → ({"type" "literal" "value" "docs"}
 ;;                   {"type" "param" "value" "slug"})
 
-(define make-route-segment
+(define make-route-segment :effects []
   (fn ((seg :as string))
     (if (and (starts-with? seg "<") (ends-with? seg ">"))
       (let ((param-name (slice seg 1 (- (len seg) 1))))
@@ -48,7 +48,7 @@
         (dict-set! d "value" seg)
         d))))
 
-(define parse-route-pattern
+(define parse-route-pattern :effects []
   (fn ((pattern :as string))
     (let ((segments (split-path-segments pattern)))
       (map make-route-segment segments))))
@@ -59,7 +59,7 @@
 ;; --------------------------------------------------------------------------
 ;; Returns params dict if match, nil if no match.
 
-(define match-route-segments
+(define match-route-segments :effects []
   (fn ((path-segs :as list) (parsed-segs :as list))
     (if (not (= (len path-segs) (len parsed-segs)))
       nil
@@ -87,7 +87,7 @@
 ;; --------------------------------------------------------------------------
 ;; Returns params dict (may be empty for exact matches) or nil.
 
-(define match-route
+(define match-route :effects []
   (fn ((path :as string) (pattern :as string))
     (let ((path-segs (split-path-segments path))
           (parsed-segs (parse-route-pattern pattern)))
@@ -100,7 +100,7 @@
 ;; Each entry: {"pattern" "/docs/<slug>" "parsed" [...] "name" "docs-page" ...}
 ;; Returns matching entry with "params" added, or nil.
 
-(define find-matching-route
+(define find-matching-route :effects []
   (fn ((path :as string) (routes :as list))
     (let ((path-segs (split-path-segments path))
           (result nil))
diff --git a/shared/sx/ref/run_type_tests.py b/shared/sx/ref/run_type_tests.py
new file mode 100644
index 0000000..d3f4021
--- /dev/null
+++ b/shared/sx/ref/run_type_tests.py
@@ -0,0 +1,180 @@
+#!/usr/bin/env python3
+"""Run test-types.sx using the bootstrapped evaluator with types module loaded."""
+from __future__ import annotations
+import os, sys
+
+_HERE = os.path.dirname(os.path.abspath(__file__))
+_PROJECT = os.path.abspath(os.path.join(_HERE, "..", "..", ".."))
+sys.path.insert(0, _PROJECT)
+
+from shared.sx.parser import parse_all
+from shared.sx.ref.sx_ref import eval_expr, trampoline, make_env
+from shared.sx.types import NIL, Component
+
+# Build env with primitives
+env = make_env()
+
+# Platform test functions
+_suite_stack: list[str] = []
+_pass_count = 0
+_fail_count = 0
+
+def _try_call(thunk):
+    try:
+        trampoline(eval_expr([thunk], env))  # call the thunk
+        return {"ok": True}
+    except Exception as e:
+        return {"ok": False, "error": str(e)}
+
+def _report_pass(name):
+    global _pass_count
+    _pass_count += 1
+    ctx = " > ".join(_suite_stack)
+    print(f"  PASS: {ctx} > {name}")
+    return NIL
+
+def _report_fail(name, error):
+    global _fail_count
+    _fail_count += 1
+    ctx = " > ".join(_suite_stack)
+    print(f"  FAIL: {ctx} > {name}: {error}")
+    return NIL
+
+def _push_suite(name):
+    _suite_stack.append(name)
+    print(f"{'  ' * (len(_suite_stack)-1)}Suite: {name}")
+    return NIL
+
+def _pop_suite():
+    if _suite_stack:
+        _suite_stack.pop()
+    return NIL
+
+env["try-call"] = _try_call
+env["report-pass"] = _report_pass
+env["report-fail"] = _report_fail
+env["push-suite"] = _push_suite
+env["pop-suite"] = _pop_suite
+
+# Test fixtures — provide the functions that tests expect
+
+# test-prim-types: dict of primitive return types for type inference
+def _test_prim_types():
+    return {
+        "+": "number", "-": "number", "*": "number", "/": "number",
+        "mod": "number", "inc": "number", "dec": "number",
+        "abs": "number", "min": "number", "max": "number",
+        "floor": "number", "ceil": "number", "round": "number",
+        "str": "string", "upper": "string", "lower": "string",
+        "trim": "string", "join": "string", "replace": "string",
+        "format": "string", "substr": "string",
+        "=": "boolean", "<": "boolean", ">": "boolean",
+        "<=": "boolean", ">=": "boolean", "!=": "boolean",
+        "not": "boolean", "nil?": "boolean", "empty?": "boolean",
+        "number?": "boolean", "string?": "boolean", "boolean?": "boolean",
+        "list?": "boolean", "dict?": "boolean", "symbol?": "boolean",
+        "keyword?": "boolean", "contains?": "boolean", "has-key?": "boolean",
+        "starts-with?": "boolean", "ends-with?": "boolean",
+        "len": "number", "first": "any", "rest": "list",
+        "last": "any", "nth": "any", "cons": "list",
+        "append": "list", "concat": "list", "reverse": "list",
+        "sort": "list", "slice": "list", "range": "list",
+        "flatten": "list", "keys": "list", "vals": "list",
+        "map-dict": "dict", "assoc": "dict", "dissoc": "dict",
+        "merge": "dict", "dict": "dict",
+        "get": "any", "type-of": "string",
+    }
+
+# test-prim-param-types: dict of primitive param type specs
+# Format: {name → {"positional" [["name" "type"] ...] "rest-type" type-or-nil}}
+def _test_prim_param_types():
+    return {
+        "+": {"positional": [["a", "number"]], "rest-type": "number"},
+        "-": {"positional": [["a", "number"]], "rest-type": "number"},
+        "*": {"positional": [["a", "number"]], "rest-type": "number"},
+        "/": {"positional": [["a", "number"]], "rest-type": "number"},
+        "inc": {"positional": [["n", "number"]], "rest-type": NIL},
+        "dec": {"positional": [["n", "number"]], "rest-type": NIL},
+        "upper": {"positional": [["s", "string"]], "rest-type": NIL},
+        "lower": {"positional": [["s", "string"]], "rest-type": NIL},
+        "keys": {"positional": [["d", "dict"]], "rest-type": NIL},
+        "vals": {"positional": [["d", "dict"]], "rest-type": NIL},
+    }
+
+# test-env: returns a fresh env for use in tests (same as the test env)
+def _test_env():
+    return env
+
+# sx-parse: parse an SX string and return list of AST nodes
+def _sx_parse(source):
+    return parse_all(source)
+
+# dict-get: used in some legacy tests
+def _dict_get(d, k):
+    v = d.get(k) if isinstance(d, dict) else NIL
+    return v if v is not None else NIL
+
+# component-set-param-types! and component-param-types: type annotation accessors
+def _component_set_param_types(comp, types_dict):
+    comp.param_types = types_dict
+    return NIL
+
+def _component_param_types(comp):
+    return getattr(comp, 'param_types', NIL)
+
+# Platform functions used by types.sx but not SX primitives
+def _component_params(c):
+    return c.params
+
+def _component_body(c):
+    return c.body
+
+def _component_has_children(c):
+    return c.has_children
+
+def _map_dict(fn, d):
+    from shared.sx.types import Lambda as _Lambda
+    result = {}
+    for k, v in d.items():
+        if isinstance(fn, _Lambda):
+            # Call SX lambda through the evaluator
+            result[k] = trampoline(eval_expr([fn, k, v], env))
+        else:
+            result[k] = fn(k, v)
+    return result
+
+env["test-prim-types"] = _test_prim_types
+env["test-prim-param-types"] = _test_prim_param_types
+env["test-env"] = _test_env
+env["sx-parse"] = _sx_parse
+env["dict-get"] = _dict_get
+env["component-set-param-types!"] = _component_set_param_types
+env["component-param-types"] = _component_param_types
+env["component-params"] = _component_params
+env["component-body"] = _component_body
+env["component-has-children"] = _component_has_children
+env["map-dict"] = _map_dict
+
+# Load test framework (macros + assertion helpers)
+with open(os.path.join(_HERE, "test-framework.sx")) as f:
+    for expr in parse_all(f.read()):
+        trampoline(eval_expr(expr, env))
+
+# Load types module
+with open(os.path.join(_HERE, "types.sx")) as f:
+    for expr in parse_all(f.read()):
+        trampoline(eval_expr(expr, env))
+
+# Run tests
+print("=" * 60)
+print("Running test-types.sx")
+print("=" * 60)
+
+with open(os.path.join(_HERE, "test-types.sx")) as f:
+    for expr in parse_all(f.read()):
+        trampoline(eval_expr(expr, env))
+
+print("=" * 60)
+print(f"Results: {_pass_count} passed, {_fail_count} failed")
+print("=" * 60)
+sys.exit(1 if _fail_count > 0 else 0)
diff --git a/shared/sx/ref/signals.sx b/shared/sx/ref/signals.sx
index 98ca89a..f7f6d11 100644
--- a/shared/sx/ref/signals.sx
+++ b/shared/sx/ref/signals.sx
@@ -41,8 +41,8 @@
 ;; 1. signal — create a reactive container
 ;; --------------------------------------------------------------------------
 
-(define signal
-  (fn (initial-value)
+(define signal :effects []
+  (fn ((initial-value :as any))
     (make-signal initial-value)))
 
 
@@ -54,8 +54,8 @@
 ;; signal as a dependency. Outside reactive context, deref just returns
 ;; the current value — no subscription, no overhead.
 
-(define deref
-  (fn (s)
+(define deref :effects []
+  (fn ((s :as any))
     (if (not (signal? s))
       s  ;; non-signal values pass through
       (let ((ctx (get-tracking-context)))
@@ -71,7 +71,7 @@
 ;; 3. reset! — write a new value, notify subscribers
 ;; --------------------------------------------------------------------------
 
-(define reset!
+(define reset! :effects [mutation]
   (fn ((s :as signal) value)
     (when (signal? s)
       (let ((old (signal-value s)))
@@ -84,7 +84,7 @@
 ;; 4. swap! — update signal via function
 ;; --------------------------------------------------------------------------
 
-(define swap!
+(define swap! :effects [mutation]
   (fn ((s :as signal) (f :as lambda) &rest args)
     (when (signal? s)
       (let ((old (signal-value s))
@@ -102,7 +102,7 @@
 ;; of its dependencies change. The dependency set is discovered automatically
 ;; by tracking deref calls during evaluation.
 
-(define computed
+(define computed :effects [mutation]
   (fn ((compute-fn :as lambda))
     (let ((s (make-signal nil))
           (deps (list))
@@ -145,7 +145,7 @@
 ;; Like computed, but doesn't produce a signal value. Returns a dispose
 ;; function that tears down the effect.
 
-(define effect
+(define effect :effects [mutation]
   (fn ((effect-fn :as lambda))
     (let ((deps (list))
           (disposed false)
@@ -201,7 +201,7 @@
 (define *batch-depth* 0)
 (define *batch-queue* (list))
 
-(define batch
+(define batch :effects [mutation]
   (fn ((thunk :as lambda))
     (set! *batch-depth* (+ *batch-depth* 1))
     (invoke thunk)
@@ -231,14 +231,14 @@
 ;;
 ;; If inside a batch, queues the signal. Otherwise, notifies immediately.
 
-(define notify-subscribers
+(define notify-subscribers :effects [mutation]
   (fn ((s :as signal))
     (if (> *batch-depth* 0)
       (when (not (contains? *batch-queue* s))
         (append! *batch-queue* s))
       (flush-subscribers s))))
 
-(define flush-subscribers
+(define flush-subscribers :effects [mutation]
   (fn ((s :as signal))
     (for-each
       (fn ((sub :as lambda)) (sub))
@@ -268,7 +268,7 @@
 ;; For computed signals, unsubscribe from all dependencies.
 ;; For effects, the dispose function is returned by effect itself.
 
-(define dispose-computed
+(define dispose-computed :effects [mutation]
   (fn ((s :as signal))
     (when (signal? s)
       (for-each
@@ -287,7 +287,7 @@
 
 (define *island-scope* nil)
 
-(define with-island-scope
+(define with-island-scope :effects [mutation]
   (fn ((scope-fn :as lambda) (body-fn :as lambda))
     (let ((prev *island-scope*))
       (set! *island-scope* scope-fn)
@@ -299,7 +299,7 @@
 ;; The platform's make-signal should call (register-in-scope s) if
 ;; *island-scope* is non-nil.
 
-(define register-in-scope
+(define register-in-scope :effects [mutation]
   (fn ((disposable :as lambda))
     (when *island-scope*
       (*island-scope* disposable))))
@@ -322,7 +322,7 @@
 ;;   (dom-set-data el key val) → void  — store JS value on element
 ;;   (dom-get-data el key)     → any   — retrieve stored value
 
-(define with-marsh-scope
+(define with-marsh-scope :effects [mutation io]
   (fn (marsh-el (body-fn :as lambda))
     ;; Execute body-fn collecting all disposables into a marsh-local list.
     ;; Nested under the current island scope — if the island is disposed,
@@ -335,7 +335,7 @@
       ;; Store disposers on the marsh element for later cleanup
       (dom-set-data marsh-el "sx-marsh-disposers" disposers))))
 
-(define dispose-marsh-scope
+(define dispose-marsh-scope :effects [mutation io]
   (fn (marsh-el)
     ;; Dispose all effects/computeds registered in this marsh's scope.
     ;; Parent island scope and sibling marshes are unaffected.
@@ -358,7 +358,7 @@
 
 (define *store-registry* (dict))
 
-(define def-store
+(define def-store :effects [mutation]
   (fn ((name :as string) (init-fn :as lambda))
     (let ((registry *store-registry*))
       ;; Only create the store once — subsequent calls return existing
@@ -366,14 +366,14 @@
         (set! *store-registry* (assoc registry name (invoke init-fn))))
       (get *store-registry* name))))
 
-(define use-store
+(define use-store :effects []
   (fn ((name :as string))
     (if (has-key? *store-registry* name)
       (get *store-registry* name)
       (error (str "Store not found: " name
                   ". Call (def-store ...) before (use-store ...).")))))
 
-(define clear-stores
+(define clear-stores :effects [mutation]
   (fn ()
     (set! *store-registry* (dict))))
 
@@ -401,11 +401,11 @@
 ;;
 ;; These are platform primitives because they require browser DOM APIs.
 
-(define emit-event
+(define emit-event :effects [io]
   (fn (el (event-name :as string) detail)
     (dom-dispatch el event-name detail)))
 
-(define on-event
+(define on-event :effects [io]
   (fn (el (event-name :as string) (handler :as lambda))
     (dom-listen el event-name handler)))
 
@@ -415,7 +415,7 @@
 ;; When the effect is disposed (island teardown), the listener is
 ;; removed automatically via the cleanup return.
 
-(define bridge-event
+(define bridge-event :effects [mutation io]
   (fn (el (event-name :as string) (target-signal :as signal) transform-fn)
     (effect (fn ()
       (let ((remove (dom-listen el event-name
@@ -449,7 +449,7 @@
 ;; Platform interface required:
 ;;   (promise-then promise on-resolve on-reject) → void
 
-(define resource
+(define resource :effects [mutation io]
   (fn ((fetch-fn :as lambda))
     (let ((state (signal (dict "loading" true "data" nil "error" nil))))
       ;; Kick off the async operation
diff --git a/shared/sx/ref/special-forms.sx b/shared/sx/ref/special-forms.sx
index 05bede7..8c880af 100644
--- a/shared/sx/ref/special-forms.sx
+++ b/shared/sx/ref/special-forms.sx
@@ -209,6 +209,29 @@
   :example "(defmacro unless (condition &rest body)
   `(when (not ~condition) ~@body))")
 
+(define-special-form "deftype"
+  :syntax (deftype name body)
+  :doc "Define a named type. The name can be a simple symbol for type aliases
+        and records, or a list (name param ...) for parameterized types.
+        Body is a type expression: a symbol (alias), (union t1 t2 ...) for
+        union types, or {:field1 type1 :field2 type2} for record types.
+        Type definitions are metadata for the type checker with no runtime cost."
+  :tail-position "none"
+  :example "(deftype price number)
+(deftype card-props {:title string :price number})
+(deftype (maybe a) (union a nil))")
+
+(define-special-form "defeffect"
+  :syntax (defeffect name)
+  :doc "Declare a named effect. Effects annotate functions and components
+        to track side effects. A pure function (:effects [pure]) cannot
+        call IO functions. Unannotated functions are assumed to have all
+        effects. Effect checking is gradual — annotations opt in."
+  :tail-position "none"
+  :example "(defeffect io)
+(defeffect async)
+(define add :effects [pure] (fn (a b) (+ a b)))")
+
 
 ;; --------------------------------------------------------------------------
 ;; Sequencing and threading
diff --git a/shared/sx/ref/sx_ref.py b/shared/sx/ref/sx_ref.py
index 71cee96..fdf007a 100644
--- a/shared/sx/ref/sx_ref.py
+++ b/shared/sx/ref/sx_ref.py
@@ -534,6 +534,11 @@ def strip_prefix(s, prefix):
     return s[len(prefix):] if s.startswith(prefix) else s
 
 
+def debug_log(*args):
+    import sys
+    print(*args, file=sys.stderr)
+
+
 def error(msg):
     raise EvalError(msg)
 
@@ -1255,6 +1260,10 @@ def eval_list(expr, env):
                 return sf_defquery(args, env)
             elif sx_truthy((name == 'defaction')):
                 return sf_defaction(args, env)
+            elif sx_truthy((name == 'deftype')):
+                return sf_deftype(args, env)
+            elif sx_truthy((name == 'defeffect')):
+                return sf_defeffect(args, env)
             elif sx_truthy((name == 'begin')):
                 return sf_begin(args, env)
             elif sx_truthy((name == 'do')):
@@ -1504,10 +1513,18 @@ def sf_lambda(args, env):
 # sf-define
 def sf_define(args, env):
     name_sym = first(args)
-    value = trampoline(eval_expr(nth(args, 1), env))
+    has_effects = ((len(args) >= 4) if not sx_truthy((len(args) >= 4)) else ((type_of(nth(args, 1)) == 'keyword') if not sx_truthy((type_of(nth(args, 1)) == 'keyword')) else (keyword_name(nth(args, 1)) == 'effects')))
+    val_idx = (3 if sx_truthy(((len(args) >= 4) if not sx_truthy((len(args) >= 4)) else ((type_of(nth(args, 1)) == 'keyword') if not sx_truthy((type_of(nth(args, 1)) == 'keyword')) else (keyword_name(nth(args, 1)) == 'effects')))) else 1)
+    value = trampoline(eval_expr(nth(args, val_idx), env))
     if sx_truthy((is_lambda(value) if not sx_truthy(is_lambda(value)) else is_nil(lambda_name(value)))):
         value.name = symbol_name(name_sym)
     env[symbol_name(name_sym)] = value
+    if sx_truthy(has_effects):
+        effects_raw = nth(args, 2)
+        effect_list = (map(lambda e: (symbol_name(e) if sx_truthy((type_of(e) == 'symbol')) else sx_str(e)), effects_raw) if sx_truthy((type_of(effects_raw) == 'list')) else [sx_str(effects_raw)])
+        effect_anns = (env_get(env, '*effect-annotations*') if sx_truthy(env_has(env, '*effect-annotations*')) else {})
+        effect_anns[symbol_name(name_sym)] = effect_list
+        env['*effect-annotations*'] = effect_anns
     return value
 
 # sf-defcomp
@@ -1522,8 +1539,14 @@ def sf_defcomp(args, env):
     param_types = nth(parsed, 2)
     affinity = defcomp_kwarg(args, 'affinity', 'auto')
     comp = make_component(comp_name, params, has_children, body, env, affinity)
+    effects = defcomp_kwarg(args, 'effects', NIL)
     if sx_truthy(((not sx_truthy(is_nil(param_types))) if not sx_truthy((not sx_truthy(is_nil(param_types)))) else (not sx_truthy(empty_p(keys(param_types)))))):
         component_set_param_types(comp, param_types)
+    if sx_truthy((not sx_truthy(is_nil(effects)))):
+        effect_list = (map(lambda e: (symbol_name(e) if sx_truthy((type_of(e) == 'symbol')) else sx_str(e)), effects) if sx_truthy((type_of(effects) == 'list')) else [sx_str(effects)])
+        effect_anns = (env_get(env, '*effect-annotations*') if sx_truthy(env_has(env, '*effect-annotations*')) else {})
+        effect_anns[symbol_name(name_sym)] = effect_list
+        env['*effect-annotations*'] = effect_anns
     env[symbol_name(name_sym)] = comp
     return comp
 
@@ -1610,6 +1633,62 @@ def sf_defstyle(args, env):
     env[symbol_name(name_sym)] = value
     return value
 
+# make-type-def
+def make_type_def(name, params, body):
+    return {'name': name, 'params': params, 'body': body}
+
+# normalize-type-body
+def normalize_type_body(body):
+    if sx_truthy(is_nil(body)):
+        return 'nil'
+    elif sx_truthy((type_of(body) == 'symbol')):
+        return symbol_name(body)
+    elif sx_truthy((type_of(body) == 'string')):
+        return body
+    elif sx_truthy((type_of(body) == 'keyword')):
+        return keyword_name(body)
+    elif sx_truthy((type_of(body) == 'dict')):
+        return map_dict(lambda k, v: normalize_type_body(v), body)
+    elif sx_truthy((type_of(body) == 'list')):
+        if sx_truthy(empty_p(body)):
+            return 'any'
+        else:
+            head = first(body)
+            head_name = (symbol_name(head) if sx_truthy((type_of(head) == 'symbol')) else sx_str(head))
+            if sx_truthy((head_name == 'union')):
+                return cons('or', map(normalize_type_body, rest(body)))
+            else:
+                return cons(head_name, map(normalize_type_body, rest(body)))
+    else:
+        return sx_str(body)
+
+# sf-deftype
+def sf_deftype(args, env):
+    name_or_form = first(args)
+    body_expr = nth(args, 1)
+    type_name = NIL
+    type_params = []
+    if sx_truthy((type_of(name_or_form) == 'symbol')):
+        type_name = symbol_name(name_or_form)
+    else:
+        if sx_truthy((type_of(name_or_form) == 'list')):
+            type_name = symbol_name(first(name_or_form))
+            type_params = map(lambda p: (symbol_name(p) if sx_truthy((type_of(p) == 'symbol')) else sx_str(p)), rest(name_or_form))
+    body = normalize_type_body(body_expr)
+    registry = (env_get(env, '*type-registry*') if sx_truthy(env_has(env, '*type-registry*')) else {})
+    registry[type_name] = make_type_def(type_name, type_params, body)
+    env['*type-registry*'] = registry
+    return NIL
+
+# sf-defeffect
+def sf_defeffect(args, env):
+    effect_name = (symbol_name(first(args)) if sx_truthy((type_of(first(args)) == 'symbol')) else sx_str(first(args)))
+    registry = (env_get(env, '*effect-registry*') if sx_truthy(env_has(env, '*effect-registry*')) else [])
+    if sx_truthy((not sx_truthy(contains_p(registry, effect_name)))):
+        registry.append(effect_name)
+    env['*effect-registry*'] = registry
+    return NIL
+
 # sf-begin
 def sf_begin(args, env):
     if sx_truthy(empty_p(args)):
@@ -1869,7 +1948,7 @@ BOOLEAN_ATTRS = ['async', 'autofocus', 'autoplay', 'checked', 'controls', 'defau
 
 # definition-form?
 def is_definition_form(name):
-    return ((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defisland') if sx_truthy((name == 'defisland')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else (name == 'defhandler'))))))
+    return ((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defisland') if sx_truthy((name == 'defisland')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else ((name == 'defhandler') if sx_truthy((name == 'defhandler')) else ((name == 'deftype') if sx_truthy((name == 'deftype')) else (name == 'defeffect'))))))))
 
 # parse-element-args
 def parse_element_args(args, env):
@@ -1995,7 +2074,7 @@ def render_value_to_html(val, env):
         return escape_html(sx_str(val))
 
 # RENDER_HTML_FORMS
-RENDER_HTML_FORMS = ['if', 'when', 'cond', 'case', 'let', 'let*', 'begin', 'do', 'define', 'defcomp', 'defisland', 'defmacro', 'defstyle', 'defhandler', 'map', 'map-indexed', 'filter', 'for-each']
+RENDER_HTML_FORMS = ['if', 'when', 'cond', 'case', 'let', 'let*', 'begin', 'do', 'define', 'defcomp', 'defisland', 'defmacro', 'defstyle', 'defhandler', 'deftype', 'defeffect', 'map', 'map-indexed', 'filter', 'for-each']
 
 # render-html-form?
 def is_render_html_form(name):
@@ -2285,7 +2364,7 @@ def aser_call(name, args, env):
     return sx_str('(', join(' ', parts), ')')
 
 # SPECIAL_FORM_NAMES
-SPECIAL_FORM_NAMES = ['if', 'when', 'cond', 'case', 'and', 'or', 'let', 'let*', 'lambda', 'fn', 'define', 'defcomp', 'defmacro', 'defstyle', 'defhandler', 'defpage', 'defquery', 'defaction', 'defrelation', 'begin', 'do', 'quote', 'quasiquote', '->', 'set!', 'letrec', 'dynamic-wind', 'defisland']
+SPECIAL_FORM_NAMES = ['if', 'when', 'cond', 'case', 'and', 'or', 'let', 'let*', 'lambda', 'fn', 'define', 'defcomp', 'defmacro', 'defstyle', 'defhandler', 'defpage', 'defquery', 'defaction', 'defrelation', 'begin', 'do', 'quote', 'quasiquote', '->', 'set!', 'letrec', 'dynamic-wind', 'defisland', 'deftype', 'defeffect']
 
 # HO_FORM_NAMES
 HO_FORM_NAMES = ['map', 'map-indexed', 'filter', 'reduce', 'some', 'every?', 'for-each']
@@ -2379,7 +2458,7 @@ def aser_special(name, expr, env):
     elif sx_truthy((name == 'defisland')):
         trampoline(eval_expr(expr, env))
         return serialize(expr)
-    elif sx_truthy(((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else ((name == 'defhandler') if sx_truthy((name == 'defhandler')) else ((name == 'defpage') if sx_truthy((name == 'defpage')) else ((name == 'defquery') if sx_truthy((name == 'defquery')) else ((name == 'defaction') if sx_truthy((name == 'defaction')) else (name == 'defrelation')))))))))):
+    elif sx_truthy(((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else ((name == 'defhandler') if sx_truthy((name == 'defhandler')) else ((name == 'defpage') if sx_truthy((name == 'defpage')) else ((name == 'defquery') if sx_truthy((name == 'defquery')) else ((name == 'defaction') if sx_truthy((name == 'defaction')) else ((name == 'defrelation') if sx_truthy((name == 'defrelation')) else ((name == 'deftype') if sx_truthy((name == 'deftype')) else (name == 'defeffect')))))))))))):
         trampoline(eval_expr(expr, env))
         return NIL
     else:
@@ -3143,7 +3222,7 @@ async def async_map_render(exprs, env, ctx):
     return results
 
 # ASYNC_RENDER_FORMS
-ASYNC_RENDER_FORMS = ['if', 'when', 'cond', 'case', 'let', 'let*', 'begin', 'do', 'define', 'defcomp', 'defisland', 'defmacro', 'defstyle', 'defhandler', 'map', 'map-indexed', 'filter', 'for-each']
+ASYNC_RENDER_FORMS = ['if', 'when', 'cond', 'case', 'let', 'let*', 'begin', 'do', 'define', 'defcomp', 'defisland', 'defmacro', 'defstyle', 'defhandler', 'deftype', 'defeffect', 'map', 'map-indexed', 'filter', 'for-each']
 
 # async-render-form?
 def async_render_form_p(name):
@@ -3518,7 +3597,7 @@ async def async_aser_call(name, args, env, ctx):
     return make_sx_expr(sx_str('(', join(' ', parts), ')'))
 
 # ASYNC_ASER_FORM_NAMES
-ASYNC_ASER_FORM_NAMES = ['if', 'when', 'cond', 'case', 'and', 'or', 'let', 'let*', 'lambda', 'fn', 'define', 'defcomp', 'defmacro', 'defstyle', 'defhandler', 'defpage', 'defquery', 'defaction', 'begin', 'do', 'quote', '->', 'set!', 'defisland']
+ASYNC_ASER_FORM_NAMES = ['if', 'when', 'cond', 'case', 'and', 'or', 'let', 'let*', 'lambda', 'fn', 'define', 'defcomp', 'defmacro', 'defstyle', 'defhandler', 'defpage', 'defquery', 'defaction', 'begin', 'do', 'quote', '->', 'set!', 'defisland', 'deftype', 'defeffect']
 
 # ASYNC_ASER_HO_NAMES
 ASYNC_ASER_HO_NAMES = ['map', 'map-indexed', 'filter', 'for-each']
@@ -3609,7 +3688,7 @@ async def dispatch_async_aser_form(name, expr, env, ctx):
     elif sx_truthy((name == 'defisland')):
         (await async_eval(expr, env, ctx))
         return serialize(expr)
-    elif sx_truthy(((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else ((name == 'defhandler') if sx_truthy((name == 'defhandler')) else ((name == 'defpage') if sx_truthy((name == 'defpage')) else ((name == 'defquery') if sx_truthy((name == 'defquery')) else (name == 'defaction'))))))))):
+    elif sx_truthy(((name == 'define') if sx_truthy((name == 'define')) else ((name == 'defcomp') if sx_truthy((name == 'defcomp')) else ((name == 'defmacro') if sx_truthy((name == 'defmacro')) else ((name == 'defstyle') if sx_truthy((name == 'defstyle')) else ((name == 'defhandler') if sx_truthy((name == 'defhandler')) else ((name == 'defpage') if sx_truthy((name == 'defpage')) else ((name == 'defquery') if sx_truthy((name == 'defquery')) else ((name == 'defaction') if sx_truthy((name == 'defaction')) else ((name == 'deftype') if sx_truthy((name == 'deftype')) else (name == 'defeffect'))))))))))):
         (await async_eval(expr, env, ctx))
         return NIL
     else:
@@ -3858,4 +3937,4 @@ def render(expr, env=None):
 
 def make_env(**kwargs):
     """Create an environment with initial bindings."""
-    return _Env(dict(kwargs))
+    return _Env(dict(kwargs))
\ No newline at end of file
diff --git a/shared/sx/ref/test-types.sx b/shared/sx/ref/test-types.sx
index 121ba23..688cb5d 100644
--- a/shared/sx/ref/test-types.sx
+++ b/shared/sx/ref/test-types.sx
@@ -427,6 +427,173 @@
           (body (first (sx-parse "(div (+ name 1))")))
           (type-env {"name" "string"})
           (diagnostics (list)))
-      (check-body-walk body "~bad-math" type-env (test-prim-types) ppt (test-env) diagnostics)
+      (check-body-walk body "~bad-math" type-env (test-prim-types) ppt (test-env) diagnostics nil nil)
       (assert-true (> (len diagnostics) 0))
       (assert-equal "error" (get (first diagnostics) "level")))))
+
+
+;; --------------------------------------------------------------------------
+;; deftype — type aliases
+;; --------------------------------------------------------------------------
+
+(defsuite "deftype-alias"
+  (deftest "simple alias resolves"
+    (let ((registry {"price" {:name "price" :params () :body "number"}}))
+      (assert-equal "number" (resolve-type "price" registry))))
+
+  (deftest "alias chain resolves"
+    (let ((registry {"price" {:name "price" :params () :body "number"}
+                     "cost" {:name "cost" :params () :body "price"}}))
+      (assert-equal "number" (resolve-type "cost" registry))))
+
+  (deftest "unknown type passes through"
+    (let ((registry {"price" {:name "price" :params () :body "number"}}))
+      (assert-equal "string" (resolve-type "string" registry))))
+
+  (deftest "subtype-resolved? works through alias"
+    (let ((registry {"price" {:name "price" :params () :body "number"}}))
+      (assert-true (subtype-resolved? "price" "number" registry))
+      (assert-true (subtype-resolved? "number" "price" registry)))))
+
+
+;; --------------------------------------------------------------------------
+;; deftype — union types
+;; --------------------------------------------------------------------------
+
+(defsuite "deftype-union"
+  (deftest "union resolves"
+    (let ((registry {"status" {:name "status" :params () :body ("or" "string" "number")}}))
+      (let ((resolved (resolve-type "status" registry)))
+        (assert-true (= (type-of resolved) "list"))
+        (assert-equal "or" (first resolved)))))
+
+  (deftest "subtype through named union"
+    (let ((registry {"status" {:name "status" :params () :body ("or" "string" "number")}}))
+      (assert-true (subtype-resolved? "string" "status" registry))
+      (assert-true (subtype-resolved? "number" "status" registry))
+      (assert-false (subtype-resolved? "boolean" "status" registry)))))
+
+
+;; --------------------------------------------------------------------------
+;; deftype — record types
+;; --------------------------------------------------------------------------
+
+(defsuite "deftype-record"
+  (deftest "record resolves to dict"
+    (let ((registry {"card-props" {:name "card-props" :params ()
+                     :body {"title" "string" "price" "number"}}}))
+      (let ((resolved (resolve-type "card-props" registry)))
+        (assert-equal "dict" (type-of resolved))
+        (assert-equal "string" (get resolved "title"))
+        (assert-equal "number" (get resolved "price")))))
+
+  (deftest "record structural subtyping"
+    (let ((registry {"card-props" {:name "card-props" :params ()
+                     :body {"title" "string" "price" "number"}}
+                     "titled" {:name "titled" :params ()
+                     :body {"title" "string"}}}))
+      ;; card-props has title+price, titled has just title
+      ;; card-props <: titled (has all required fields)
+      (assert-true (subtype-resolved? "card-props" "titled" registry))))
+
+  (deftest "get infers field type from record"
+    (let ((registry {"card-props" {:name "card-props" :params ()
+                     :body {"title" "string" "price" "number"}}})
+          (type-env {"d" "card-props"})
+          (expr (first (sx-parse "(get d :title)"))))
+      (assert-equal "string"
+        (infer-type expr type-env (test-prim-types) registry)))))
+
+
+;; --------------------------------------------------------------------------
+;; deftype — parameterized types
+;; --------------------------------------------------------------------------
+
+(defsuite "deftype-parameterized"
+  (deftest "maybe instantiation"
+    (let ((registry {"maybe" {:name "maybe" :params ("a")
+                     :body ("or" "a" "nil")}}))
+      (let ((resolved (resolve-type (list "maybe" "string") registry)))
+        (assert-true (= (type-of resolved) "list"))
+        (assert-equal "or" (first resolved))
+        (assert-true (contains? resolved "string"))
+        (assert-true (contains? resolved "nil")))))
+
+  (deftest "subtype through parameterized type"
+    (let ((registry {"maybe" {:name "maybe" :params ("a")
+                     :body ("or" "a" "nil")}}))
+      (assert-true (subtype-resolved? "string" (list "maybe" "string") registry))
+      (assert-true (subtype-resolved? "nil" (list "maybe" "string") registry))
+      (assert-false (subtype-resolved? "number" (list "maybe" "string") registry))))
+
+  (deftest "substitute-type-vars works"
+    (let ((result (substitute-type-vars ("or" "a" "nil") (list "a") (list "number"))))
+      (assert-equal "or" (first result))
+      (assert-true (contains? result "number"))
+      (assert-true (contains? result "nil")))))
+
+
+;; --------------------------------------------------------------------------
+;; defeffect — effect basics
+;; --------------------------------------------------------------------------
+
+(defsuite "defeffect-basics"
+  (deftest "get-effects returns nil for unannotated"
+    (let ((anns {"fetch" ("io")}))
+      (assert-true (nil? (get-effects "unknown" anns)))))
+
+  (deftest "get-effects returns effects for annotated"
+    (let ((anns {"fetch" ("io")}))
+      (assert-equal (list "io") (get-effects "fetch" anns))))
+
+  (deftest "nil annotations returns nil"
+    (assert-true (nil? (get-effects "anything" nil)))))
+
+
+;; --------------------------------------------------------------------------
+;; defeffect — effect checking
+;; --------------------------------------------------------------------------
+
+(defsuite "effect-checking"
+  (deftest "pure cannot call io"
+    (let ((anns {"~pure-comp" () "fetch" ("io")}))
+      (let ((diagnostics (check-effect-call "fetch" (list) anns "~pure-comp")))
+        (assert-true (> (len diagnostics) 0))
+        (assert-equal "error" (get (first diagnostics) "level")))))
+
+  (deftest "io context allows io"
+    (let ((anns {"~io-comp" ("io") "fetch" ("io")}))
+      (let ((diagnostics (check-effect-call "fetch" (list "io") anns "~io-comp")))
+        (assert-equal 0 (len diagnostics)))))
+
+  (deftest "unannotated caller allows everything"
+    (let ((anns {"fetch" ("io")}))
+      (let ((diagnostics (check-effect-call "fetch" nil anns "~unknown")))
+        (assert-equal 0 (len diagnostics)))))
+
+  (deftest "unannotated callee skips check"
+    (let ((anns {"~pure-comp" ()}))
+      (let ((diagnostics (check-effect-call "unknown-fn" (list) anns "~pure-comp")))
+        (assert-equal 0 (len diagnostics))))))
+
+
+;; --------------------------------------------------------------------------
+;; defeffect — subset checking
+;; --------------------------------------------------------------------------
+
+(defsuite "effect-subset"
+  (deftest "empty is subset of anything"
+    (assert-true (effects-subset? (list) (list "io")))
+    (assert-true (effects-subset? (list) (list))))
+
+  (deftest "io is subset of io"
+    (assert-true (effects-subset? (list "io") (list "io" "async"))))
+
+  (deftest "io is not subset of pure"
+    (assert-false (effects-subset? (list "io") (list))))
+
+  (deftest "nil callee skips check"
+    (assert-true (effects-subset? nil (list))))
+
+  (deftest "nil caller allows all"
+    (assert-true (effects-subset? (list "io") nil))))
diff --git a/shared/sx/ref/types.sx b/shared/sx/ref/types.sx
index 63e4370..e552757 100644
--- a/shared/sx/ref/types.sx
+++ b/shared/sx/ref/types.sx
@@ -224,7 +224,7 @@
 ;; type-env is a dict mapping variable names → types.
 
 (define infer-type
-  (fn (node (type-env :as dict) (prim-types :as dict))
+  (fn (node (type-env :as dict) (prim-types :as dict) type-registry)
     (let ((kind (type-of node)))
       (if (= kind "number")  "number"
       (if (= kind "string")  "string"
@@ -234,24 +234,24 @@
       (if (= kind "symbol")
         (let ((name (symbol-name node)))
           ;; Look up in type env
-          (if (dict-has? type-env name)
-            (dict-get type-env name)
+          (if (has-key? type-env name)
+            (get type-env name)
             ;; Builtins
             (if (= name "true") "boolean"
               (if (= name "false") "boolean"
                 (if (= name "nil") "nil"
                   ;; Check primitive return types
-                  (if (dict-has? prim-types name)
-                    (dict-get prim-types name)
+                  (if (has-key? prim-types name)
+                    (get prim-types name)
                     "any"))))))
       (if (= kind "dict") "dict"
       (if (= kind "list")
-        (infer-list-type node type-env prim-types)
+        (infer-list-type node type-env prim-types type-registry)
         "any")))))))))))
 
 
 (define infer-list-type
-  (fn (node (type-env :as dict) (prim-types :as dict))
+  (fn (node (type-env :as dict) (prim-types :as dict) type-registry)
     ;; Infer type of a list expression (function call, special form, etc.)
     (if (empty? node) "list"
       (let ((head (first node))
@@ -261,32 +261,32 @@
           (let ((name (symbol-name head)))
             ;; Special forms
             (if (= name "if")
-              (infer-if-type args type-env prim-types)
+              (infer-if-type args type-env prim-types type-registry)
             (if (= name "when")
               (if (>= (len args) 2)
-                (type-union (infer-type (last args) type-env prim-types) "nil")
+                (type-union (infer-type (last args) type-env prim-types type-registry) "nil")
                 "nil")
             (if (or (= name "cond") (= name "case"))
               "any"   ;; complex — could be refined later
             (if (= name "let")
-              (infer-let-type args type-env prim-types)
+              (infer-let-type args type-env prim-types type-registry)
             (if (or (= name "do") (= name "begin"))
               (if (empty? args) "nil"
-                (infer-type (last args) type-env prim-types))
+                (infer-type (last args) type-env prim-types type-registry))
             (if (or (= name "lambda") (= name "fn"))
               "lambda"
             (if (= name "and")
               (if (empty? args) "boolean"
-                (infer-type (last args) type-env prim-types))
+                (infer-type (last args) type-env prim-types type-registry))
             (if (= name "or")
               (if (empty? args) "boolean"
                 ;; or returns first truthy — union of all args
                 (reduce type-union "never"
-                  (map (fn (a) (infer-type a type-env prim-types)) args)))
+                  (map (fn (a) (infer-type a type-env prim-types type-registry)) args)))
             (if (= name "map")
               ;; map returns a list
               (if (>= (len args) 2)
-                (let ((fn-type (infer-type (first args) type-env prim-types)))
+                (let ((fn-type (infer-type (first args) type-env prim-types type-registry)))
                   ;; If the fn's return type is known, produce (list-of return-type)
                   (if (and (= (type-of fn-type) "list")
                            (= (first fn-type) "->"))
@@ -296,7 +296,7 @@
             (if (= name "filter")
               ;; filter preserves element type
               (if (>= (len args) 2)
-                (infer-type (nth args 1) type-env prim-types)
+                (infer-type (nth args 1) type-env prim-types type-registry)
                 "list")
             (if (= name "reduce")
               ;; reduce returns the accumulator type — too complex to infer
@@ -311,26 +311,45 @@
               "string"
             (if (= name "not")
               "boolean"
+            (if (= name "get")
+              ;; get — resolve record field type from type registry
+              (if (and (>= (len args) 2) (not (nil? type-registry)))
+                (let ((dict-type (infer-type (first args) type-env prim-types type-registry))
+                      (key-arg (nth args 1))
+                      (key-name (cond
+                                  (= (type-of key-arg) "keyword") (keyword-name key-arg)
+                                  (= (type-of key-arg) "string") key-arg
+                                  :else nil)))
+                  (if (and key-name
+                           (= (type-of dict-type) "string")
+                           (has-key? type-registry dict-type))
+                    (let ((resolved (resolve-type dict-type type-registry)))
+                      (if (and (= (type-of resolved) "dict")
+                               (has-key? resolved key-name))
+                        (get resolved key-name)
+                        "any"))
+                    "any"))
+                "any")
             (if (starts-with? name "~")
               "element"   ;; component call
               ;; Regular function call: look up return type
-              (if (dict-has? prim-types name)
-                (dict-get prim-types name)
-                "any"))))))))))))))))))))))))
+              (if (has-key? prim-types name)
+                (get prim-types name)
+                "any")))))))))))))))))))))))))
 
 
 (define infer-if-type
-  (fn ((args :as list) (type-env :as dict) (prim-types :as dict))
+  (fn ((args :as list) (type-env :as dict) (prim-types :as dict) type-registry)
     ;; (if test then else?) → union of then and else types
     (if (< (len args) 2) "nil"
-      (let ((then-type (infer-type (nth args 1) type-env prim-types)))
+      (let ((then-type (infer-type (nth args 1) type-env prim-types type-registry)))
         (if (>= (len args) 3)
-          (type-union then-type (infer-type (nth args 2) type-env prim-types))
+          (type-union then-type (infer-type (nth args 2) type-env prim-types type-registry))
           (type-union then-type "nil"))))))
 
 
 (define infer-let-type
-  (fn ((args :as list) (type-env :as dict) (prim-types :as dict))
+  (fn ((args :as list) (type-env :as dict) (prim-types :as dict) type-registry)
     ;; (let ((x expr) ...) body) → type of body in extended type-env
     (if (< (len args) 2) "nil"
       (let ((bindings (first args))
@@ -343,10 +362,10 @@
               (let ((name (if (= (type-of (first binding)) "symbol")
                             (symbol-name (first binding))
                             (str (first binding))))
-                    (val-type (infer-type (nth binding 1) extended prim-types)))
+                    (val-type (infer-type (nth binding 1) extended prim-types type-registry)))
                 (dict-set! extended name val-type))))
           bindings)
-        (infer-type body extended prim-types)))))
+        (infer-type body extended prim-types type-registry)))))
 
 
 ;; --------------------------------------------------------------------------
@@ -371,14 +390,14 @@
 ;; --------------------------------------------------------------------------
 
 (define check-primitive-call
-  (fn ((name :as string) (args :as list) (type-env :as dict) (prim-types :as dict) prim-param-types (comp-name :as string))
+  (fn ((name :as string) (args :as list) (type-env :as dict) (prim-types :as dict) prim-param-types (comp-name :as string) type-registry)
     ;; Check a primitive call site against declared param types.
     ;; prim-param-types is a dict: {prim-name → {:positional [...] :rest-type type-or-nil}}
     ;; Each positional entry is a list (name type-or-nil).
     ;; Returns list of diagnostics.
     (let ((diagnostics (list)))
       (when (and (not (nil? prim-param-types))
-                 (dict-has? prim-param-types name))
+                 (has-key? prim-param-types name))
         (let ((sig (get prim-param-types name))
               (positional (get sig "positional"))
               (rest-type (get sig "rest-type")))
@@ -392,10 +411,10 @@
                         (arg-expr (nth args idx)))
                     (let ((expected-type (nth param-info 1)))
                       (when (not (nil? expected-type))
-                        (let ((actual (infer-type arg-expr type-env prim-types)))
+                        (let ((actual (infer-type arg-expr type-env prim-types type-registry)))
                           (when (and (not (type-any? expected-type))
                                      (not (type-any? actual))
-                                     (not (subtype? actual expected-type)))
+                                     (not (subtype-resolved? actual expected-type type-registry)))
                             (append! diagnostics
                               (make-diagnostic "error"
                                 (str "Argument " (+ idx 1) " of `" name
@@ -404,10 +423,10 @@
                   ;; Rest param — check against rest-type
                   (when (not (nil? rest-type))
                     (let ((arg-expr (nth args idx))
-                          (actual (infer-type arg-expr type-env prim-types)))
+                          (actual (infer-type arg-expr type-env prim-types type-registry)))
                       (when (and (not (type-any? rest-type))
                                  (not (type-any? actual))
-                                 (not (subtype? actual rest-type)))
+                                 (not (subtype-resolved? actual rest-type type-registry)))
                         (append! diagnostics
                           (make-diagnostic "error"
                             (str "Argument " (+ idx 1) " of `" name
@@ -418,7 +437,7 @@
 
 
 (define check-component-call
-  (fn ((comp-name :as string) (comp :as component) (call-args :as list) (type-env :as dict) (prim-types :as dict))
+  (fn ((comp-name :as string) (comp :as component) (call-args :as list) (type-env :as dict) (prim-types :as dict) type-registry)
     ;; Check a component call site against its declared param types.
     ;; comp is the component value, call-args is the list of args
     ;; from the call site (after the component name).
@@ -440,12 +459,12 @@
                       (when (< (+ idx 1) (len call-args))
                         (let ((val-expr (nth call-args (+ idx 1))))
                           ;; Check type of value against declared param type
-                          (when (dict-has? param-types key-name)
-                            (let ((expected (dict-get param-types key-name))
-                                  (actual (infer-type val-expr type-env prim-types)))
+                          (when (has-key? param-types key-name)
+                            (let ((expected (get param-types key-name))
+                                  (actual (infer-type val-expr type-env prim-types type-registry)))
                               (when (and (not (type-any? expected))
                                          (not (type-any? actual))
-                                         (not (subtype? actual expected)))
+                                         (not (subtype-resolved? actual expected type-registry)))
                                 (append! diagnostics
                                   (make-diagnostic "error"
                                     (str "Keyword :" key-name " of " comp-name
@@ -456,9 +475,9 @@
           ;; Check for missing required params (those with declared types)
           (for-each
             (fn (param-name)
-              (when (and (dict-has? param-types param-name)
+              (when (and (has-key? param-types param-name)
                          (not (contains? provided-keys param-name))
-                         (not (type-nullable? (dict-get param-types param-name))))
+                         (not (type-nullable? (get param-types param-name))))
                 (append! diagnostics
                   (make-diagnostic "warning"
                     (str "Required param :" param-name " of " comp-name " not provided")
@@ -482,9 +501,11 @@
 ;; --------------------------------------------------------------------------
 
 (define check-body-walk
-  (fn (node (comp-name :as string) (type-env :as dict) (prim-types :as dict) prim-param-types env (diagnostics :as list))
+  (fn (node (comp-name :as string) (type-env :as dict) (prim-types :as dict) prim-param-types env (diagnostics :as list) type-registry effect-annotations)
     ;; Recursively walk an AST and collect diagnostics.
     ;; prim-param-types: dict of {name → {:positional [...] :rest-type t}} or nil
+    ;; type-registry: dict of {type-name → type-def} or nil
+    ;; effect-annotations: dict of {fn-name → effect-list} or nil
     (let ((kind (type-of node)))
       (when (= kind "list")
         (when (not (empty? node))
@@ -500,16 +521,30 @@
                       (for-each
                         (fn (d) (append! diagnostics d))
                         (check-component-call name comp-val args
-                          type-env prim-types)))))
+                          type-env prim-types type-registry))))
+                  ;; Effect check for component calls
+                  (when (not (nil? effect-annotations))
+                    (let ((caller-effects (get-effects comp-name effect-annotations)))
+                      (for-each
+                        (fn (d) (append! diagnostics d))
+                        (check-effect-call name caller-effects effect-annotations comp-name)))))
 
                 ;; Primitive call — check param types
                 (when (and (not (starts-with? name "~"))
                            (not (nil? prim-param-types))
-                           (dict-has? prim-param-types name))
+                           (has-key? prim-param-types name))
                   (for-each
                     (fn (d) (append! diagnostics d))
                     (check-primitive-call name args type-env prim-types
-                      prim-param-types comp-name)))
+                      prim-param-types comp-name type-registry)))
+
+                ;; Effect check for function calls
+                (when (and (not (starts-with? name "~"))
+                           (not (nil? effect-annotations)))
+                  (let ((caller-effects (get-effects comp-name effect-annotations)))
+                    (for-each
+                      (fn (d) (append! diagnostics d))
+                      (check-effect-call name caller-effects effect-annotations comp-name))))
 
                 ;; Recurse into let with extended type env
                 (when (or (= name "let") (= name "let*"))
@@ -524,12 +559,12 @@
                             (let ((bname (if (= (type-of (first binding)) "symbol")
                                            (symbol-name (first binding))
                                            (str (first binding))))
-                                  (val-type (infer-type (nth binding 1) extended prim-types)))
+                                  (val-type (infer-type (nth binding 1) extended prim-types type-registry)))
                               (dict-set! extended bname val-type))))
                         bindings)
                       (for-each
                         (fn (body)
-                          (check-body-walk body comp-name extended prim-types prim-param-types env diagnostics))
+                          (check-body-walk body comp-name extended prim-types prim-param-types env diagnostics type-registry effect-annotations))
                         body-exprs))))
 
                 ;; Recurse into define with type binding
@@ -541,13 +576,13 @@
                           (def-val (nth args 1)))
                       (when def-name
                         (dict-set! type-env def-name
-                          (infer-type def-val type-env prim-types)))
-                      (check-body-walk def-val comp-name type-env prim-types prim-param-types env diagnostics))))))
+                          (infer-type def-val type-env prim-types type-registry)))
+                      (check-body-walk def-val comp-name type-env prim-types prim-param-types env diagnostics type-registry effect-annotations))))))
 
             ;; Recurse into all child expressions
             (for-each
               (fn (child)
-                (check-body-walk child comp-name type-env prim-types prim-param-types env diagnostics))
+                (check-body-walk child comp-name type-env prim-types prim-param-types env diagnostics type-registry effect-annotations))
               args)))))))
 
 
@@ -556,9 +591,11 @@
 ;; --------------------------------------------------------------------------
 
 (define check-component
-  (fn ((comp-name :as string) env (prim-types :as dict) prim-param-types)
+  (fn ((comp-name :as string) env (prim-types :as dict) prim-param-types type-registry effect-annotations)
     ;; Type-check a component's body. Returns list of diagnostics.
     ;; prim-param-types: dict of param type info, or nil to skip primitive checking.
+    ;; type-registry: dict of {type-name → type-def} or nil
+    ;; effect-annotations: dict of {fn-name → effect-list} or nil
     (let ((comp (env-get env comp-name))
           (diagnostics (list)))
       (when (= (type-of comp) "component")
@@ -572,15 +609,15 @@
             (fn (p)
               (dict-set! type-env p
                 (if (and (not (nil? param-types))
-                         (dict-has? param-types p))
-                  (dict-get param-types p)
+                         (has-key? param-types p))
+                  (get param-types p)
                   "any")))
             params)
           ;; Add children as (list-of element) if component has children
           (when (component-has-children comp)
             (dict-set! type-env "children" (list "list-of" "element")))
 
-          (check-body-walk body comp-name type-env prim-types prim-param-types env diagnostics)))
+          (check-body-walk body comp-name type-env prim-types prim-param-types env diagnostics type-registry effect-annotations)))
       diagnostics)))
 
 
@@ -589,9 +626,11 @@
 ;; --------------------------------------------------------------------------
 
 (define check-all
-  (fn (env (prim-types :as dict) prim-param-types)
+  (fn (env (prim-types :as dict) prim-param-types type-registry effect-annotations)
     ;; Type-check every component in the environment.
     ;; prim-param-types: dict of param type info, or nil to skip primitive checking.
+    ;; type-registry: dict of {type-name → type-def} or nil
+    ;; effect-annotations: dict of {fn-name → effect-list} or nil
     ;; Returns list of all diagnostics.
     (let ((all-diagnostics (list)))
       (for-each
@@ -600,7 +639,7 @@
             (when (= (type-of val) "component")
               (for-each
                 (fn (d) (append! all-diagnostics d))
-                (check-component name env prim-types prim-param-types)))))
+                (check-component name env prim-types prim-param-types type-registry effect-annotations)))))
         (keys env))
       all-diagnostics)))
 
@@ -619,21 +658,208 @@
     (let ((registry (dict)))
       (for-each
         (fn (decl)
-          (let ((name (dict-get decl "name"))
-                (returns (dict-get decl "returns")))
+          (let ((name (get decl "name"))
+                (returns (get decl "returns")))
             (when (and (not (nil? name)) (not (nil? returns)))
               (dict-set! registry name returns))))
         prim-declarations)
       (for-each
         (fn (decl)
-          (let ((name (dict-get decl "name"))
-                (returns (dict-get decl "returns")))
+          (let ((name (get decl "name"))
+                (returns (get decl "returns")))
             (when (and (not (nil? name)) (not (nil? returns)))
               (dict-set! registry name returns))))
         io-declarations)
       registry)))
 
 
+;; --------------------------------------------------------------------------
+;; 13. User-defined types (deftype)
+;; --------------------------------------------------------------------------
+;; Type definitions are plain dicts: {:name "price" :params [] :body "number"}
+;; Stored in env under "*type-registry*" mapping type names to defs.
+
+;; make-type-def and normalize-type-body are defined in eval.sx
+;; (always compiled). They're available when types.sx is compiled as a spec module.
+
+;; -- Standard type definitions --
+;; These define the record types used throughout the type system itself.
+
+;; Universal: nullable shorthand
+(deftype (maybe a) (union a nil))
+
+;; A type definition entry in the registry
+(deftype type-def
+  {:name string :params list :body any})
+
+;; A diagnostic produced by the type checker
+(deftype diagnostic
+  {:level string :message string :component string? :expr any})
+
+;; Primitive parameter type signature
+(deftype prim-param-sig
+  {:positional list :rest-type string?})
+
+;; Effect declarations
+(defeffect io)
+(defeffect mutation)
+(defeffect render)
+
+(define type-def-name
+  (fn (td) (get td "name")))
+
+(define type-def-params
+  (fn (td) (get td "params")))
+
+(define type-def-body
+  (fn (td) (get td "body")))
+
+(define resolve-type
+  (fn (t registry)
+    ;; Resolve a type through the registry.
+    ;; Returns the resolved type representation.
+    (if (nil? registry) t
+      (cond
+        ;; String — might be a named type alias
+        (= (type-of t) "string")
+          (if (has-key? registry t)
+            (let ((td (get registry t)))
+              (let ((params (type-def-params td))
+                    (body (type-def-body td)))
+                (if (empty? params)
+                  ;; Simple alias — resolve the body recursively
+                  (resolve-type body registry)
+                  ;; Parameterized with no args — return as-is
+                  t)))
+            t)
+        ;; List — might be parameterized type application or compound
+        (= (type-of t) "list")
+          (if (empty? t) t
+            (let ((head (first t)))
+              (cond
+                ;; (or ...), (list-of ...), (-> ...) — recurse into members
+                (or (= head "or") (= head "list-of") (= head "->")
+                    (= head "dict-of"))
+                  (cons head (map (fn (m) (resolve-type m registry)) (rest t)))
+                ;; Parameterized type application: ("maybe" "string") etc.
+                (and (= (type-of head) "string")
+                     (has-key? registry head))
+                  (let ((td (get registry head))
+                        (params (type-def-params td))
+                        (body (type-def-body td))
+                        (args (rest t)))
+                    (if (= (len params) (len args))
+                      (resolve-type
+                        (substitute-type-vars body params args)
+                        registry)
+                      ;; Wrong arity — return as-is
+                      t))
+                :else t)))
+        ;; Dict — record type, resolve field types
+        (= (type-of t) "dict")
+          (map-dict (fn (k v) (resolve-type v registry)) t)
+        ;; Anything else — return as-is
+        :else t))))
+
+(define substitute-type-vars
+  (fn (body (params :as list) (args :as list))
+    ;; Substitute type variables in body.
+    ;; params is a list of type var names, args is corresponding types.
+    (let ((subst (dict)))
+      (for-each
+        (fn (i)
+          (dict-set! subst (nth params i) (nth args i)))
+        (range 0 (len params) 1))
+      (substitute-in-type body subst))))
+
+(define substitute-in-type
+  (fn (t (subst :as dict))
+    ;; Recursively substitute type variables.
+    (cond
+      (= (type-of t) "string")
+        (if (has-key? subst t) (get subst t) t)
+      (= (type-of t) "list")
+        (map (fn (m) (substitute-in-type m subst)) t)
+      (= (type-of t) "dict")
+        (map-dict (fn (k v) (substitute-in-type v subst)) t)
+      :else t)))
+
+(define subtype-resolved?
+  (fn (a b registry)
+    ;; Resolve both sides through the registry, then check subtype.
+    (if (nil? registry)
+      (subtype? a b)
+      (let ((ra (resolve-type a registry))
+            (rb (resolve-type b registry)))
+        ;; Handle record structural subtyping: dict a <: dict b
+        ;; if every field in b exists in a with compatible type
+        (if (and (= (type-of ra) "dict") (= (type-of rb) "dict"))
+          (every?
+            (fn (key)
+              (and (has-key? ra key)
+                   (subtype-resolved? (get ra key) (get rb key) registry)))
+            (keys rb))
+          (subtype? ra rb))))))
+
+
+;; --------------------------------------------------------------------------
+;; 14. Effect checking (defeffect)
+;; --------------------------------------------------------------------------
+;; Effects are annotations on functions/components describing their
+;; side effects. A pure function cannot call IO functions.
+
+(define get-effects
+  (fn ((name :as string) effect-annotations)
+    ;; Look up declared effects for a function/component.
+    ;; Returns list of effect strings, or nil if unannotated.
+    (if (nil? effect-annotations) nil
+      (if (has-key? effect-annotations name)
+        (get effect-annotations name)
+        nil))))
+
+(define effects-subset?
+  (fn (callee-effects caller-effects)
+    ;; Are all callee effects allowed by caller?
+    ;; nil effects = unannotated = assumed to have all effects.
+    ;; Empty list = pure = no effects.
+    (if (nil? caller-effects) true     ;; unannotated caller allows everything
+      (if (nil? callee-effects) true   ;; unannotated callee — skip check
+        (every?
+          (fn (e) (contains? caller-effects e))
+          callee-effects)))))
+
+(define check-effect-call
+  (fn ((callee-name :as string) caller-effects effect-annotations (comp-name :as string))
+    ;; Check that callee's effects are allowed by caller's effects.
+    ;; Returns list of diagnostics.
+    (let ((diagnostics (list))
+          (callee-effects (get-effects callee-name effect-annotations)))
+      (when (and (not (nil? caller-effects))
+                 (not (nil? callee-effects))
+                 (not (effects-subset? callee-effects caller-effects)))
+        (append! diagnostics
+          (make-diagnostic "error"
+            (str "`" callee-name "` has effects "
+                 (join ", " callee-effects)
+                 " but `" comp-name "` only allows "
+                 (if (empty? caller-effects) "[pure]"
+                   (join ", " caller-effects)))
+            comp-name nil)))
+      diagnostics)))
+
+(define build-effect-annotations
+  (fn ((io-declarations :as list))
+    ;; Assign [io] effect to all IO primitives.
+    (let ((annotations (dict)))
+      (for-each
+        (fn (decl)
+          (let ((name (get decl "name")))
+            (when (not (nil? name))
+              (dict-set! annotations name (list "io")))))
+        io-declarations)
+      annotations)))
+
+
 ;; --------------------------------------------------------------------------
 ;; Platform interface summary
 ;; --------------------------------------------------------------------------