From 1144015fe3028e62dbe4ae380425ce5aa8ecfdc1 Mon Sep 17 00:00:00 2001
From: Raymond Toy <toy.raymond@gmail.com>
Date: Sun, 10 Jan 2021 04:33:03 +0000
Subject: [PATCH] Fix #91: Handle loop destructuring

The destructuring shortcut in loop doesn't require all the parts be
available.  If they're not, each item is replaced by NIL.

This is fixed by still using `destructuring-bind`, except we mark
everything as optional.
---
 src/code/loop.lisp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/code/loop.lisp b/src/code/loop.lisp
index 8e50390b7..6325f239d 100644
--- a/src/code/loop.lisp
+++ b/src/code/loop.lisp
@@ -995,7 +995,10 @@ collected result will be returned as the value of the LOOP."
   (if crocks
       (let ((*ignores* ()))
 	(declare (special *ignores*))
-	`((destructuring-bind ,(subst-gensyms-for-nil (car crocks))
+	;; Destructuring in loop doesn't require that the values be
+	;; available.  The missing elements are filled with NIL.  So,
+	;; make everything &optional
+	`((destructuring-bind (&optional ,@(subst-gensyms-for-nil (car crocks)))
 	      ,(cadr crocks)
 	    (declare (ignore ,@*ignores*))
 	    ,@(loop-build-destructuring-bindings (cddr crocks) forms))))
-- 
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