Fix cond ambiguity: check ALL clauses with cond-scheme?, not just first

The cond special form misclassified Clojure-style as scheme-style when
the first test was a 2-element list like (nil? x) — treating it as a
scheme clause ((test body)) instead of a function call. Define
cond-scheme? using every? to check ALL clauses, fix eval.sx sf-cond and
render.sx eval-cond, rewrite engine.sx parse-time/filter-params as
nested if to avoid the ambiguity, add regression tests across eval/
render/aser specs. 378/378 tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/bootstrap_py.py

@@ -539,6 +539,9 @@ class PyEmitter:
         clauses = expr[1:]
         if not clauses:
             return "NIL"
+        # Check ALL clauses are 2-element lists (scheme-style).
+        # Checking only the first is ambiguous — (nil? x) is a 2-element
+        # function call, not a scheme clause ((test body)).
         is_scheme = (
             all(isinstance(c, list) and len(c) == 2 for c in clauses)
             and not any(isinstance(c, Keyword) for c in clauses)

shared/sx/ref/engine.sx

@@ -34,11 +34,12 @@
 (define parse-time
   (fn (s)
     ;; Parse time string: "2s" → 2000, "500ms" → 500
-    (cond
-      (nil? s) 0
-      (ends-with? s "ms") (parse-int s 0)
-      (ends-with? s "s")  (* (parse-int (replace s "s" "") 0) 1000)
-      :else (parse-int s 0))))
+    ;; Uses nested if (not cond) because cond misclassifies 2-element
+    ;; function calls like (nil? s) as scheme-style ((test body)) clauses.
+    (if (nil? s) 0
+      (if (ends-with? s "ms") (parse-int s 0)
+        (if (ends-with? s "s") (* (parse-int (replace s "s" "") 0) 1000)
+          (parse-int s 0))))))
 
 
 (define parse-trigger-spec
@@ -219,20 +220,19 @@
     ;; Filter form parameters by sx-params spec.
     ;; all-params is a list of (key value) pairs.
     ;; Returns filtered list of (key value) pairs.
-    (cond
-      (nil? params-spec) all-params
-      (= params-spec "none") (list)
-      (= params-spec "*") all-params
-      (starts-with? params-spec "not ")
-        (let ((excluded (map trim (split (slice params-spec 4) ","))))
-          (filter
-            (fn (p) (not (contains? excluded (first p))))
-            all-params))
-      :else
-        (let ((allowed (map trim (split params-spec ","))))
-          (filter
-            (fn (p) (contains? allowed (first p)))
-            all-params)))))
+    ;; Uses nested if (not cond) — see parse-time comment.
+    (if (nil? params-spec) all-params
+      (if (= params-spec "none") (list)
+        (if (= params-spec "*") all-params
+          (if (starts-with? params-spec "not ")
+            (let ((excluded (map trim (split (slice params-spec 4) ","))))
+              (filter
+                (fn (p) (not (contains? excluded (first p))))
+                all-params))
+            (let ((allowed (map trim (split params-spec ","))))
+              (filter
+                (fn (p) (contains? allowed (first p)))
+                all-params))))))))
 
 
 ;; --------------------------------------------------------------------------

shared/sx/ref/eval.sx

@@ -309,14 +309,18 @@
         nil))))
 
 
+;; cond-scheme? — check if ALL clauses are 2-element lists (scheme-style).
+;; Checking only the first arg is ambiguous — (nil? x) is a 2-element
+;; function call, not a scheme clause ((test body)).
+(define cond-scheme?
+  (fn (clauses)
+    (every? (fn (c) (and (= (type-of c) "list") (= (len c) 2)))
+            clauses)))
+
 (define sf-cond
   (fn (args env)
-    ;; Detect scheme-style: first arg is a 2-element list
-    (if (and (= (type-of (first args)) "list")
-             (= (len (first args)) 2))
-      ;; Scheme-style: ((test body) ...)
+    (if (cond-scheme? args)
       (sf-cond-scheme args env)
-      ;; Clojure-style: test body test body ...
       (sf-cond-clojure args env))))
 
 (define sf-cond-scheme

shared/sx/ref/render.sx

@@ -134,12 +134,8 @@
 ;; (test body test body ...).
 (define eval-cond
   (fn (clauses env)
-    (if (and (not (empty? clauses))
-             (= (type-of (first clauses)) "list")
-             (= (len (first clauses)) 2))
-      ;; Scheme-style
+    (if (cond-scheme? clauses)
       (eval-cond-scheme clauses env)
-      ;; Clojure-style
       (eval-cond-clojure clauses env))))
 
 (define eval-cond-scheme

shared/sx/ref/sx_ref.py

@@ -1357,9 +1357,13 @@ def sf_when(args, env):
     else:
         return NIL
 
+# cond-scheme?
+def cond_scheme_p(clauses):
+    return every_p(lambda c: ((type_of(c) == 'list') if not sx_truthy((type_of(c) == 'list')) else (len(c) == 2)), clauses)
+
 # sf-cond
 def sf_cond(args, env):
-    if sx_truthy(((type_of(first(args)) == 'list') if not sx_truthy((type_of(first(args)) == 'list')) else (len(first(args)) == 2))):
+    if sx_truthy(cond_scheme_p(args)):
         return sf_cond_scheme(args, env)
     else:
         return sf_cond_clojure(args, env)
@@ -1859,7 +1863,7 @@ def render_attrs(attrs):
 
 # eval-cond
 def eval_cond(clauses, env):
-    if sx_truthy(((not sx_truthy(empty_p(clauses))) if not sx_truthy((not sx_truthy(empty_p(clauses)))) else ((type_of(first(clauses)) == 'list') if not sx_truthy((type_of(first(clauses)) == 'list')) else (len(first(clauses)) == 2)))):
+    if sx_truthy(cond_scheme_p(clauses)):
         return eval_cond_scheme(clauses, env)
     else:
         return eval_cond_clojure(clauses, env)
@@ -3833,4 +3837,4 @@ def render(expr, env=None):
 
 def make_env(**kwargs):
     """Create an environment with initial bindings."""
-    return _Env(dict(kwargs))
+    return _Env(dict(kwargs))

shared/sx/ref/test-aser.sx

@@ -115,6 +115,13 @@
     (assert-equal "(p \"two\")"
       (render-sx "(cond false (p \"one\") true (p \"two\") :else (p \"three\"))")))
 
+  (deftest "cond with 2-element predicate test"
+    ;; Regression: cond misclassifies (nil? x) as scheme-style clause.
+    (assert-equal "(p \"yes\")"
+      (render-sx "(cond (nil? nil) (p \"yes\") :else (p \"no\"))"))
+    (assert-equal "(p \"no\")"
+      (render-sx "(cond (nil? \"x\") (p \"yes\") :else (p \"no\"))")))
+
   (deftest "let binds then serializes"
     (assert-equal "(p \"hello\")"
       (render-sx "(let ((x \"hello\")) (p x))")))

shared/sx/ref/test-eval.sx

@@ -277,6 +277,29 @@
                         false "b"
                         :else "c")))
 
+  (deftest "cond with 2-element predicate as first test"
+    ;; Regression: cond misclassifies Clojure-style as scheme-style when
+    ;; the first test is a 2-element list like (nil? x) or (empty? x).
+    ;; The evaluator checks: is first arg a 2-element list? If yes, treats
+    ;; as scheme-style ((test body) ...) — returning the arg instead of
+    ;; evaluating the predicate call.
+    (assert-equal 0 (cond (nil? nil) 0 :else 1))
+    (assert-equal 1 (cond (nil? "x") 0 :else 1))
+    (assert-equal "empty" (cond (empty? (list)) "empty" :else "not-empty"))
+    (assert-equal "not-empty" (cond (empty? (list 1)) "empty" :else "not-empty"))
+    (assert-equal "yes" (cond (not false) "yes" :else "no"))
+    (assert-equal "no" (cond (not true) "yes" :else "no")))
+
+  (deftest "cond with 2-element predicate and no :else"
+    ;; Same bug, but without :else — this is the worst case because the
+    ;; bootstrapper heuristic also breaks (all clauses are 2-element lists).
+    (assert-equal "found"
+      (cond (nil? nil) "found"
+            (nil? "x") "other"))
+    (assert-equal "b"
+      (cond (nil? "x") "a"
+            (not false) "b")))
+
   (deftest "and"
     (assert-true (and true true))
     (assert-false (and true false))

shared/sx/ref/test-render.sx

@@ -151,6 +151,13 @@
     (assert-equal "<p>hello</p>"
       (render-html "(let ((x \"hello\")) (p x))")))
 
+  (deftest "cond with 2-element predicate test"
+    ;; Regression: cond misclassifies (nil? x) as scheme-style clause.
+    (assert-equal "<p>yes</p>"
+      (render-html "(cond (nil? nil) (p \"yes\") :else (p \"no\"))"))
+    (assert-equal "<p>no</p>"
+      (render-html "(cond (nil? \"x\") (p \"yes\") :else (p \"no\"))")))
+
   (deftest "let preserves outer scope bindings"
     ;; Regression: process-bindings must preserve parent env scope chain.
     ;; Using merge() on Env objects returns empty dict (Env is not dict subclass).