added: call-by-value interpreter

Author: yinwang0

encoding.scm

@@ -83,5 +83,5 @@
 
 
 ;; example use:
-(decode-number (eval `(,! ,lfive)))
+;; (decode-number (eval `(,! ,lfive)))
 

interp-call-by-value.ss

@@ -0,0 +1,67 @@
+;; A call-by-value interpreter for lambda calculus with primitive operators
+
+;; author: Yin Wang ([email protected])
+
+
+(load "pmatch.scm")
+(load "encoding.scm")
+
+
+;; environment
+(define env0 '())
+
+(define ext-env
+  (lambda (x v env)
+    (cons `(,x . ,v) env)))
+
+(define lookup
+  (lambda (x env)
+    (let ([p (assq x env)])
+      (cond
+       [(not p) x]
+       [else (cdr p)]))))
+
+
+;; closure "structure"
+(define make-closure
+  (lambda (f env)
+    (list 'closure f env)))
+
+(define closure-func cadr)
+(define closure-env caddr)
+
+(define closure?
+  (lambda (x)
+    (and (pair? x)
+         (eq? (car x) 'closure))))
+
+
+
+;; cbv interpreter
+(define interp1
+  (lambda (exp env)
+    (pmatch exp
+      [,x (guard (symbol? x)) (lookup x env)]
+      [,x (guard (number? x)) x]
+      [(lambda (,x) ,e)
+       (make-closure exp env)]
+      [(,e1 ,e2)
+       (let ([v1 (interp1 e1 env)]
+             [v2 (interp1 e2 env)])
+         (pmatch v1
+           [(closure (lambda (,x) ,e) ,env1)
+            (interp1 e (ext-env x v2 env1))]
+           [,other
+            (eval `(,v1 ,v2))]))]
+      [,exp (eval exp)])))
+
+
+(define interp
+  (lambda (exp)
+    (interp1 exp env0)))
+
+
+
+;; ------------------------ tests -------------------------
+(interp `(((,ltwo ,ltwo) add1) 1))
+;; => 5