From 37c881d461e55d5c5115c6c6ed397a3df8913fd2 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 11 Nov 2016 22:08:33 -0800
Subject: Clause in case{q,ql,qual} with no forms yields nil.

* eval.c (me_case): If forms is nil, substitute
the object (nil) for forms, to ensure a nil result
through the expansion to a cond.

* txr.1: Documented and added compat notes.
---
 eval.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'eval.c')

diff --git a/eval.c b/eval.c
index f863e5fd..e0c852b0 100644
--- a/eval.c
+++ b/eval.c
@@ -3132,6 +3132,7 @@ static val me_case(val form, val menv)
   val testform = pop(&form);
   val tformsym = gensym(lit("test-"));
   val memfuncsym, eqfuncsym;
+  val lofnil = cons(nil, nil);
   list_collect_decl (condpairs, ptail);
 
   if (casesym == caseq_s) {
@@ -3167,12 +3168,13 @@ static val me_case(val form, val menv)
                                      nao),
                                 forms));
     } else {
+      uses_or2;
       ptail = list_collect(ptail,
                            cons(list(if3(atom(keys), eqfuncsym, memfuncsym),
                                      tformsym,
                                      list(quote_s, keys, nao),
                                      nao),
-                                forms));
+                                or2(forms, lofnil)));
     }
   }
 
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