bug: symbol-value place always global.

We have a problem. If v is a dynamic variable, then
the form

  (let (v)
    (set (symbol-value 'v) 3))

is not behaving correctly; it's updating the top-level
value of v not the rebound one.

* eval.c (set_symbol_value): New static function.
(eval_init): Register sys:set-symbol-value intrinsic.
The top-vb variable, though no longer referenced by
the symbol-value place, because existing compiled
code depends on it.

* stdlib/place.tl (symbol-value): Rewrite the place
logic to use symbol-value to access the variable,
and set-symbol-value to update it, instead of referencing
sys:top-vb.
(sys:get-vb): This function has to stay, because it
provides run-time support for code compiled with the
buggy version of the place.

* tests/019/symbol-value.tl: New file.

1 files changed, 4 insertions, 4 deletions

diff --git a/stdlib/place.tl b/stdlib/place.tl
index 13b9bb18..fdd4e544 100644
--- a/stdlib/place.tl
+++ b/stdlib/place.tl
@@ -862,10 +862,10 @@
 
 (defplace (symbol-value sym-expr) body
   (getter setter
-    (with-gensyms (binding-sym)
-      ^(let ((,binding-sym (sys:get-vb ,sym-expr)))
-          (macrolet ((,getter () ^(cdr ,',binding-sym))
-                     (,setter (val) ^(sys:rplacd ,',binding-sym ,val)))
+    (with-gensyms (sym)
+      ^(let ((,sym ,sym-expr))
+          (macrolet ((,getter () ^(symbol-value ,',sym))
+                     (,setter (val) ^(sys:set-symbol-value ,',sym ,val)))
             ,body))))
   nil
   (deleter