Allow symbol macro in function call dot position.

* eval.c (expand_forms): If the forms list is an atom, then
don't just return it. Try to expand it as a macro.
If the macro produces a compound form, diagnose with
an exception, otherwise return the expansion.

* txr.1: Document the treatment of symbol macros in
function call dot position.

1 files changed, 14 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index b030b9b7..62ffe92c 100644
--- a/txr.1
+++ b/txr.1
@@ -10079,6 +10079,20 @@ Examples:
   (call (op list 1 . @1) 2) ;; yields 2
 .cble
 
+A special consideration is given to symbol macros which occur in the
+dot position. If a symbol macro occurs in this position, then it must not
+expand to a compound form, otherwise a macro-expansion-time error results.
+If it expands to an atom, then it is substituted by that atom, and
+the semantics of the function call proceeds as described above.
+
+.cblk
+  (symacrolet ((x (list 1 2)))
+    (list 1 . x))  ;; error: x expands to form (list 1 2)
+
+  (symacrolet ((x 2))
+    (list 1 . x))  ;; yields (1 . 2)
+.cble
+
 Dialect Note:
 
 In some other Lisp dialects like ANSI Common Lisp, the improper list syntax may