Add FLUID-LET.

standard.virtua

@@ -159,6 +159,12 @@
         (eval (list* (setter (eval cmb env)) value args) env))
       (eval (list $set! place value) env)))
 
+(defmacro fluid-let ((name value) . body) env
+  (let ((saved-value (eval name env)))
+    (eval (list set! name value) env)
+    (unwind-protect (eval (list* begin body) env)
+      (eval (list set! name saved-value) env))))
+
 (defun setter (obj) (get-slot obj "setter"))
 (defun set-setter! (obj setter) (set-slot! obj "setter" setter))
 (set-setter! js-global (lambda (val name) (set-js-global! name val))) ; erm

test.virtua

@@ -159,6 +159,17 @@
 
 (assert (= "foobar" (strcat "foo" "bar")))
 
+(scope
+   (def x 1)
+   (fluid-let (x 2)
+     (assert (= x 2)))
+   (assert (= x 1))
+   (block exit
+     (fluid-let (x 3)
+       (assert (= x 3))
+       (return-from exit)))
+   (assert (= x 1)))
+
 ;;;; Options
 
 (assert (= 12 (if-option (name (option 12)) name 13)))