Implement till 4.11

misc/evaluator.scm

@@ -159,4 +159,77 @@
                      (sequence->exp (cond-actions first))
                      (expand-clauses rest))))))
 
+(define (true? x)
+  (not (eq? x false)))
+(define (false? x)
+  (eq? x false))
+
+(define (make-procedure parameters body env)
+  (list 'procedure parameters body env))
+(define (compound-procedure? p)
+  (tagged-list? p 'procedure))
+(define (procedure-parameters p) (cadr p))
+(define (procedure-body p) (caddr p))
+(define (procedure-environment p) (cadddr p))
+
+(define (enclosing-environment env) (cdr env))
+(define (first-frame env) (car env))
+(define the-empty-environment '())
+
+(define (make-frame variables values)
+  (cons variables values))
+(define (frame-variables frame) (car frame))
+(define (frame-values frame) (cdr frame))
+(define (add-binding-to-frame! var val frame)
+  (set-car! frame (cons var (car frame)))
+  (set-cdr! frame (cons val (cdr frame))))
+
+(define (extend-environment vars vals base-env)
+  (if (= (length vars) (length vals))
+      (cons (make-frame vars vals) base-env)
+      (if (< (length vars) (length vals))
+          (error "Too many arguments supplied" vars vals)
+          (error "Too few arguments supplied" vars vals))))
+
+(define (lookup-variable-value var env)
+  (define (env-loop env)
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (env-loop (enclosing-environment env)))
+            ((eq? var (car vars))
+             (car vals))
+            (else (scan (cdr vars) (cdr vals)))))
+    (if (eq? env the-empty-environment)
+        (error "Unbound variable" var)
+        (let ((frame (first-frame env)))
+          (scan (frame-variables frame)
+                (frame-values frame)))))
+  (env-loop env))
+
+(define (set-variable-value! var val env)
+  (define (env-loop env)
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (env-loop (enclosing-environment env)))
+            ((eq? var (car vars))
+             (set-car! vals val))
+            (else (scan (cdr vars) (cdr vals)))))
+    (if (eq? env the-empty-environment)
+        (error "Unbound variable -- SET!" var)
+        (let ((frame (first-frame env)))
+          (scan (frame-variables frame)
+                (frame-values frame)))))
+  (env-loop env))
+
+(define (define-variable! var val env)
+  (let ((frame (first-frame env)))
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (add-binding-to-frame! var val frame))
+            ((eq? var (car vars))
+             (set-car! vals val))
+            (else (scan (cdr vars) (cdr vals)))))
+    (scan (frame-variables frame)
+          (frame-values frame))))
+
 'evaluator-loaded