match undefined hygienically wrapper forward refs on define (fixes issue #399)

eval.c

@@ -150,6 +150,15 @@ sexp sexp_env_cell_define (sexp ctx, sexp env, sexp key,
     if (sexp_car(ls) == key) {
       sexp_cdr(ls) = value;
       return ls;
+    } else if (sexp_cdr(ls) == SEXP_UNDEF &&
+               sexp_synclop(sexp_car(ls)) &&
+               sexp_synclo_env(sexp_car(ls)) == env &&
+               sexp_synclo_expr(sexp_car(ls)) == key) {
+      /* handle an undefined renamed reference that would have */
+      /* resolved to this binding, renamed to what we define here */
+      sexp_car(ls) = key;
+      sexp_cdr(ls) = value;
+      return ls;
     }
   sexp_gc_preserve2(ctx, cell, ls);
   sexp_env_push(ctx, env, cell, key, value);

tests/r7rs-tests.scm

@@ -540,6 +540,16 @@
                   '#(b)))))
   (test '#(b) (vector-lit)))
 
+(let ()
+  ;; forward hygienic refs
+  (define-syntax foo399
+    (syntax-rules () ((foo399) (bar399))))
+  (define (quux399)
+    (foo399))
+  (define (bar399)
+    42)
+  (test 42 (quux399)))
+
 (test-end)
 
 (test-begin "5 Program structure")