Spec eval-cond and process-bindings in render.sx (remove platform implementations)

eval-cond and process-bindings were hand-written platform JS in
bootstrap_js.py rather than specced in .sx files. This violated the
SX host architecture principle. Now specced in render.sx as shared
render adapter helpers, bootstrapped to both JS and Python.

eval-cond handles both scheme-style ((test body) ...) and clojure-style
(test body test body ...) cond clauses. Returns unevaluated body
expression for the adapter to render in its own mode.

process-bindings evaluates let-binding pairs and returns extended env.

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

shared/sx/ref/render.sx

@@ -124,6 +124,75 @@
         (keys attrs)))))
 
 
+;; --------------------------------------------------------------------------
+;; Render adapter helpers
+;; --------------------------------------------------------------------------
+;; Shared by HTML and DOM adapters for evaluating control forms during
+;; rendering. Unlike sf-cond (eval.sx) which returns a thunk for TCO,
+;; eval-cond returns the unevaluated body expression so the adapter
+;; can render it in its own mode (HTML string vs DOM nodes).
+
+;; 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
+  (fn (clauses env)
+    (if (and (not (empty? clauses))
+             (= (type-of (first clauses)) "list")
+             (= (len (first clauses)) 2))
+      ;; Scheme-style
+      (eval-cond-scheme clauses env)
+      ;; Clojure-style
+      (eval-cond-clojure clauses env))))
+
+(define eval-cond-scheme
+  (fn (clauses env)
+    (if (empty? clauses)
+      nil
+      (let ((clause (first clauses))
+            (test   (first clause))
+            (body   (nth clause 1)))
+        (if (or (and (= (type-of test) "symbol")
+                     (or (= (symbol-name test) "else")
+                         (= (symbol-name test) ":else")))
+                (and (= (type-of test) "keyword")
+                     (= (keyword-name test) "else")))
+          body
+          (if (trampoline (eval-expr test env))
+            body
+            (eval-cond-scheme (rest clauses) env)))))))
+
+(define eval-cond-clojure
+  (fn (clauses env)
+    (if (< (len clauses) 2)
+      nil
+      (let ((test (first clauses))
+            (body (nth clauses 1)))
+        (if (or (and (= (type-of test) "keyword") (= (keyword-name test) "else"))
+                (and (= (type-of test) "symbol")
+                     (or (= (symbol-name test) "else")
+                         (= (symbol-name test) ":else"))))
+          body
+          (if (trampoline (eval-expr test env))
+            body
+            (eval-cond-clojure (slice clauses 2) env)))))))
+
+;; process-bindings: evaluate let-binding pairs, return extended env.
+;; bindings = ((name1 expr1) (name2 expr2) ...)
+(define process-bindings
+  (fn (bindings env)
+    (let ((local (merge env)))
+      (for-each
+        (fn (pair)
+          (when (and (= (type-of pair) "list") (>= (len pair) 2))
+            (let ((name (if (= (type-of (first pair)) "symbol")
+                          (symbol-name (first pair))
+                          (str (first pair)))))
+              (env-set! local name (trampoline (eval-expr (nth pair 1) local))))))
+        bindings)
+      local)))
+
+
 ;; --------------------------------------------------------------------------
 ;; Platform interface (shared across adapters)
 ;; --------------------------------------------------------------------------