From ae1a2aa6be47998f2de8601ae77daf5b4cdb18fe Mon Sep 17 00:00:00 2001
From: Alex Shinn <alexshinn@gmail.com>
Date: Sun, 26 Mar 2017 21:16:36 +0900
Subject: [PATCH] match undefined hygienically wrapper forward refs on define
 (fixes issue #399)

---
 eval.c               |  9 +++++++++
 tests/r7rs-tests.scm | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/eval.c b/eval.c
index 30bc6713..fd3af251 100644
--- a/eval.c
+++ b/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);
diff --git a/tests/r7rs-tests.scm b/tests/r7rs-tests.scm
index 4c39bd9d..e08412ff 100644
--- a/tests/r7rs-tests.scm
+++ b/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")