Symbol macros.

* eval.c (top_smb, defsymacro_s, symacrolet_s): New global variables.
(lookup_symac, get_opt_param_syms, get_param_syms, op_defsymacro,
expand_symacrolet, make_var_shadowing_env): New static functions.
(expand_tree_cases, expand_catch_clause): Install shadowing environment
so lexical bindings hide any symbol macrolets.
(expand_place): Fix neglect to expand an atomic form, which breaks
symbol macros used as places.
(expand): Expand symbol macros, expand symacrolet binding forms.
Make sure symbol macros are shadowed in the lexical binding
constructs. Take advantage of return value of rlcp_tree in a
few places.
(macro_form_p): Support for symbol macros; bugfix: not handling
default argument.
(macroexpand_1): Streamlined, and support added for symbol macros.
(eval_init): Protect top_smb from gc. Create new hash, stored in
top_smb. Initialize defsymacro_s and symacrolet_s.
Register op_defsymacro.

* parser.y (rlcp_tree): Return the to form instead of useless t and nil.

* txr.1: Documented.

1 files changed, 3 insertions, 4 deletions

diff --git a/parser.y b/parser.y
index 819630b9..3ea01e43 100644
--- a/parser.y
+++ b/parser.y
@@ -1153,15 +1153,14 @@ val rlset(val form, val info)
 
 val rlcp_tree(val to, val from)
 {
-  if (atom(to)) {
-    return nil;
-  } else {
+  val ret = to;
+  if (consp(to)) {
     if (!source_loc(to))
       rlcp(to, from);
     for (; consp(to); to = cdr(to))
       rlcp_tree(car(to), from);
-    return t;
   }
+  return ret;
 }
 
 static wchar_t char_from_name(const wchar_t *name)