From f8555f796d8e4f077cab2e9edc8f2e028a74513b Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Thu, 21 Jul 2022 21:41:47 -0400
Subject: [PATCH] Issue #489 - Guarantee order of eval begin exprs

Guarantee that sub-expressions of a begin are evaluated in order. The code was reversing the results of a map. However map is not necessarily guaranteed to evaluate its arguments in any given order because it could be optimized into another function such as `Cyc-map-loop-1`. Instead we just use the optimized function directly as a more general `map` is not required here and this function is guaranteed to process its argument list in a predicable order.
---
 CHANGELOG.md    |  4 ++++
 scheme/eval.sld | 11 +++--------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 08c46d2f..cd48329c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,10 @@ Features
 
 Bug Fixes
 
+- Prevent an error when evaluating a `begin` expression that contains both a macro definition and an application of that macro. For example:
+
+      begin (define-syntax foo (syntax-rules () ((foo) 123))) (foo))
+
 - Fix a regression where `c-compiler-options` was not recognized as a top level form by programs.
 - Enforce a maximum recursion depth when printing an object via `display` and `write`, and when comparing objects via `equal?`. This prevents segmentation faults when working with circular data structures.
 
diff --git a/scheme/eval.sld b/scheme/eval.sld
index f45ec40a..ba33ae11 100644
--- a/scheme/eval.sld
+++ b/scheme/eval.sld
@@ -636,14 +636,9 @@
 ;(display "/* ")
 ;(write (list exp))
 ;(display "*/ ")
-       (let ((fncs 
-               ;; Our map starts from the end, we reverse
-               ;; so everything is evaluated in order, then
-               ;; reverse again so results are in order
-               (reverse
-                 (map (lambda (expr) 
-                        (analyze expr a-env rename-env local-renamed))
-                      (reverse (cdr exp))))))
+       (let ((fncs (Cyc-map-loop-1 (lambda (expr) 
+                                      (analyze expr a-env rename-env local-renamed))
+                                   (cdr exp))))
          (lambda (env)
            (foldl (lambda (fnc _) (fnc env)) #f fncs))))
       ;; compiled macro