first 3 interpreters

Author: Yin Wang

calculator.ss

@@ -0,0 +1,22 @@
+(define tree-sum
+  (lambda (exp)
+    (match exp
+      [(? number? x) x]
+      [`(,e1 ,e2)
+       (let ([v1 (tree-sum e1)]
+             [v2 (tree-sum e2)])
+         (+ v1 v2))])))
+
+
+
+(tree-sum '(1 2))
+;; => 3
+
+(tree-sum '(1 (2 3)))
+;; => 6
+
+(tree-sum '((1 2) 3))
+;; => 6
+
+(tree-sum '((1 2) (3 4)))
+;; => 10

r2-interpreter.ss

@@ -0,0 +1,45 @@
+#lang racket
+
+(struct Closure (f env))
+
+(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)]))))
+
+(define interp
+  (lambda (exp env)
+    (match exp
+      [(? symbol? x) (lookup x env)]
+      [(? number? x) x]
+      [`(lambda (,x) ,e)
+       (Closure exp env)]
+      [`(let ([,x ,e1]) ,e2)
+       (let ([v1 (interp e1 env)])
+         (interp e2 (ext-env x v1 env)))]
+      [`(,e1 ,e2)
+       (let ([v1 (interp e1 env)]
+             [v2 (interp e2 env)])
+         (match v1
+           [(Closure `(lambda (,x) ,e) env-save)
+            (interp e (ext-env x v2 env-save))]))]
+      [`(,op ,e1 ,e2)
+       (let ([v1 (interp e1 env)]
+             [v2 (interp e2 env)])
+         (match op
+           ['+ (+ v1 v2)]
+           ['- (- v1 v2)]
+           ['* (* v1 v2)]
+           ['/ (/ v1 v2)]))])))
+
+(define interpreter
+  (lambda (exp)
+    (interp exp env0)))

r3-interpreter.ss

@@ -0,0 +1,75 @@
+#lang racket
+
+(struct Scope (table parent))
+(struct Closure (f env))
+
+(define env0 (Scope (make-hash) #f))
+
+(define ext-env
+  (lambda (env)
+    (let* ([new-hash (make-hash)]
+           [new-env (Scope new-hash env)])
+      new-env)))
+
+(define def
+  (lambda (x v env)
+    (hash-set! (Scope-table env) x v)))
+
+(define bind
+  (lambda (x v env)
+    (let (new-env (ext-env env))
+      (def x v new-env)
+      new-env)))
+
+(define lookup
+  (lambda (x env)
+    (cond
+     [(not env) #f]
+     [else
+      (let ([v? (hash-ref (Scope-table env) x #f)])
+        (cond
+         [(not v?)
+          (lookup x (Scope-parent env))]
+         [else v?]))])))
+
+(define interp
+  (lambda (exp env)
+    (match exp
+      [(? symbol? x)
+       (let ([v (lookup x env)])
+         (cond
+          [(not v)
+           (error "undefined variable" x)]
+          [else v]))]
+      [(? number? x) x]
+      [`(lambda (,x) ,e)
+       (Closure exp env)]
+      [`(let ([,x ,e1]) ,e2)
+       (let ([v1 (interp e1 env)])
+         (interp e2 (ext-env x v1 env)))]
+      [`(define ,x ,e)
+       (let ([v1 (interp e env)])
+         (def x v1 env))]
+      [`(begin ,e1 ... ,en)
+       (for ([e e1])
+         (interp e env))
+       (interp en env)]
+      [`(,e1 ,e2)
+       (let ([v1 (interp e1 env)]
+             [v2 (interp e2 env)])
+         (match v1
+           [(Closure `(lambda (,x) ,e) env-save)
+            (interp e (ext-env x v2 env-save))]))]
+      [`(,op ,e1 ,e2)
+       (let ([v1 (interp e1 env)]
+             [v2 (interp e2 env)])
+         (match op
+           ['+ (+ v1 v2)]
+           ['- (- v1 v2)]
+           ['* (* v1 v2)]
+           ['/ (/ v1 v2)]))])))
+
+
+(define interpreter
+  (lambda (exp)
+    (interp exp env0)))