Bugfix in case{q,ql,qual} macro expansion.

* eval.c (me_case): The key must be quoted unconditionally
whether it's an atom or list. Let's make this subject
to the compatibility flag in case someone's code depends
on it.

* txr.1: Compat notes added.

2 files changed, 35 insertions, 6 deletions

diff --git a/eval.c b/eval.c
index b6503280..f863e5fd 100644
--- a/eval.c
+++ b/eval.c
@@ -3157,12 +3157,23 @@ static val me_case(val form, val menv)
     if (keys == t)
       eval_error(form_orig, lit("~s: symbol t used as key"), casesym, nao);
 
-    ptail = list_collect(ptail,
-                         cons(list(if3(atom(keys), eqfuncsym, memfuncsym),
-                                   tformsym,
-                                   if3(atom(keys), keys, list(quote_s, keys, nao)),
-                                   nao),
-                              forms));
+    if (opt_compat && opt_compat <= 156) {
+      ptail = list_collect(ptail,
+                           cons(list(if3(atom(keys), eqfuncsym, memfuncsym),
+                                     tformsym,
+                                     if3(atom(keys),
+                                         keys,
+                                         list(quote_s, keys, nao)),
+                                     nao),
+                                forms));
+    } else {
+      ptail = list_collect(ptail,
+                           cons(list(if3(atom(keys), eqfuncsym, memfuncsym),
+                                     tformsym,
+                                     list(quote_s, keys, nao),
+                                     nao),
+                                forms));
+    }
   }
 
   if (form && atom(form))
diff --git a/txr.1 b/txr.1
index 39be55b9..054cd670 100644
--- a/txr.1
+++ b/txr.1
@@ -49312,6 +49312,24 @@ of these version values, the described behaviors are provided if
 is given an argument which is equal or lower. For instance
 .code "-C 103"
 selects the behaviors described below for version 105, but not those for 102.
+.IP 156
+After version 156, a bug was fixed in the macro expander for
+.codn caseq ,
+.code caseql
+and
+.codn casequal .
+Selecting a compatibility value of 156 or less restores the buggy
+behavior. The bug was that single-atom case keys were undergoing
+evaluation. For instance
+.code "(caseql x (a 0))"
+would arrange for the evaluation of
+.code a
+as a variable, rather than treating it as the symbol
+.code a
+itself. Beside using the compatibility mechanism, a workaround is to
+use a list of keys, exemplified by a rewrite of the foregoing
+expression to
+.codn "(caseql x ((a) 0))" .
 .IP 155
 After version 155, the
 .code tok-str