symbol-function semantics change; new symbol-macro.

* eval.c (symbol_function): Only retrieve function binding,
and not macro or operator bindings, unless compatibility
<= 127 is in effect.
(symbol_macro): New function.
(fboundp): Only test for existence of function, not
macro or operator, unless <= 127 compatibility is in effect.
(fmakunbound): Do not remove macro binding, unless
compatibility <= 127 is in effect.
(eval_init): Register sys:top-mb variable for use in place.tl
library module. Register symbol-macro intrinsic function.

* share/txr/stdlib/place.tl (sys:get-mb): New function
(symbol-macro): New syntactic place.

* txr.1: Updated incorrect documentation about environments
from the perspective that macros and functions coexist.
Documented symbol-macro. Updated symbol-function, fboundp
and fmakunbound documentation. Added missing documentation
for mmakunbound. Reference to fboundp under define-place-macro
revised to mboundp.  Added compatibility notes.

1 files changed, 16 insertions, 0 deletions

diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl
index 29c8e1fa..02a5c653 100644
--- a/share/txr/stdlib/place.tl
+++ b/share/txr/stdlib/place.tl
@@ -584,6 +584,22 @@
     ^(macrolet ((,deleter () ^(fmakunbound ,',sym-expr)))
        ,body)))
 
+(defun sys:get-mb (sym)
+  (or (gethash sys:top-mb sym)
+      (sys:eval-err "unbound macro ~s" sym)))
+
+(defplace (symbol-macro sym-expr) body
+  (getter setter
+    (with-gensyms (binding-sym)
+      ^(let ((,binding-sym (sys:get-mb ,sym-expr)))
+          (macrolet ((,getter () ^(cdr ,',binding-sym))
+                     (,setter (val) ^(sys:rplacd ,',binding-sym ,val)))
+            ,body))))
+  :
+  (deleter
+    ^(macrolet ((,deleter () ^(mmakunbound ,',sym-expr)))
+       ,body)))
+
 (defun sys:get-vb (sym)
   (or (gethash sys:top-vb sym)
       (sys:eval-err "unbound variable ~s" sym)))