haskell: classic program fib.hs + source-order top-level binding (+2 tests, 388/388)

lib/haskell/eval.sx

@@ -677,16 +677,22 @@ plus a b = a + b
   hk-bind-decls!
   (fn
     (env decls)
-    (let ((groups (dict)) (pat-binds (list)))
-      ;; Pass 1: collect fun-clause groups by name; collect pat-binds
-      ;; in source order. Pre-seed env so any name can already be
-      ;; looked up by closures built in pass 2.
+    (let
+      ((groups (dict))
+        (group-order (list))
+        (pat-binds (list)))
+      ;; Pass 1: collect fun-clause groups by name; track first-seen
+      ;; order so pass 3 can evaluate 0-arity bodies in source order
+      ;; (forward references to other 0-arity definitions still need
+      ;; the earlier name to be bound first).
       (for-each
         (fn (d)
           (cond
             ((= (first d) "fun-clause")
               (let
                 ((name (nth d 1)))
+                (when (not (has-key? groups name))
+                  (append! group-order name))
                 (dict-set!
                   groups
                   name
@@ -703,8 +709,9 @@ plus a b = a + b
               (append! pat-binds d))
             (:else nil)))
         decls)
-      ;; Pass 2: install multifuns for arity > 0; mark 0-arity for
-      ;; pass 3. The mutable env means recursive references work.
+      ;; Pass 2: install multifuns (arity > 0) — order doesn't matter
+      ;; because they're closures; collect 0-arity names in source
+      ;; order for pass 3.
       (let ((zero-arity (list)))
         (for-each
           (fn (name)
@@ -717,8 +724,11 @@ plus a b = a + b
                       name
                       (hk-mk-multifun arity clauses env)))
                   (:else (append! zero-arity name))))))
-          (keys groups))
-        ;; Pass 3: evaluate 0-arity bodies and pat-binds.
+          group-order)
+        ;; Pass 3: evaluate 0-arity bodies and pat-binds in source
+        ;; order — forward references to a later 0-arity name will
+        ;; still see its placeholder (nil) and fail noisily, but the
+        ;; common case of a top-down program works.
         (for-each
           (fn (name)
             (let ((clauses (get groups name)))