fisl

commit 5ff7353e5f4508d427c30baee6233140b5c71a7a (patch)
parent e98c287ec33108ff0904f5391fc3de4ed9f1d948
Author: Alex Karle <alex@alexkarle.com>
Date:   Fri, 18 Nov 2022 12:08:59 -0500

assignment: Fix assignment vs definition bug

I had intermingled assignment and definition such that

var x = 5;

and

x = 5;

did the same thing, when really the first should create a new binding
in the current environment and the second should update the value in
*whichever environment has x defined (the closest one)*.

This was found while implementing 'while' since the following was an
infinite loop:

var x = 10;
while (x > 0) {
    print x;
    x = x - 1;
}

With the splitting of var -> env-def! and = -> env-set! in this patch,
it works as expected!

Diffstat:
M
interpreter.scm
 | 
15
+++++++++++++--

1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/interpreter.scm b/interpreter.scm
@@ -15,9 +15,17 @@
 		   (if parent
 		       (env-get parent el)
 		       (runtime-err! (format "Unbound variable ~A" el))))))
-	    ((eq? action 'set)
+	    ((eq? action 'def)
+	     ;; var block, sets in current env
 	     (lambda (el val)
 	       (hash-table-set! ht el val)))
+	    ((eq? action 'set)
+	     (lambda (el val)
+	       (if (hash-table-exists? ht el)
+		   (hash-table-set! ht el val)
+		   (if parent
+		       (env-set! parent el val)
+		       (runtime-err! (format "Unable to set unbound variable ~A" el))))))
 	    ((eq? action 'exists)
 	     (lambda (el)
 	       (if (hash-table-exists? ht el)
@@ -31,6 +39,9 @@
 (define (env-set! env key val)
   ((env 'set) key val))
 
+(define (env-def! env key val)
+  ((env 'def) key val))
+
 (define (env-exists? env key)
   ((env 'exists) key))
 
@@ -145,7 +156,7 @@
             (if (null? (var-stmt-init stmt))
               '()
               (evaluate (var-stmt-init stmt) env))))
-      (env-set! env (token-lexeme (var-stmt-name stmt)) value))
+      (env-def! env (token-lexeme (var-stmt-name stmt)) value))
     '())
    ((expr-stmt? stmt)
     (let ((res (evaluate (expr-stmt-value stmt) env)))