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, 24 insertions, 0 deletions

diff --git a/tests/019/symbol-value.tl b/tests/019/symbol-value.tl
new file mode 100644
index 00000000..ca724f5a
--- /dev/null
+++ b/tests/019/symbol-value.tl
@@ -0,0 +1,24 @@
+(load "../common")
+
+(defparm v 42)
+
+(mtest
+  v 42
+  (symbol-value 'v) 42
+  (set (symbol-value 'v) 73) 73
+  (symbol-value 'v) 73
+  v 73)
+
+(mtest
+  (let ((v 2)) v) 2
+  (let ((v 2)) (symbol-value 'v)) 2
+  (progn (let ((v 2)) (set (symbol-value 'v) 1)) v) 73
+  (let ((v 2)) (set (symbol-value 'v) 1) v) 1
+  v 73)
+
+(test
+  (progn
+    (let ((v 2))
+      (set (symbol-value 'x) 73))
+    x)
+  73)