Port c2 to rvar

c2.rkt

@@ -1,43 +0,0 @@
-#lang racket
-
-(require racket/fixnum)
-
-(provide interp-R1 interp-exp env-head-value env-head-symbol eval-symbol add-binding)
-
-(define (interp-R1 env)
-  (lambda (p)
-    (match p
-       [`(program ,data ,exp) ((interp-exp env) exp)])))
-
-(define (interp-exp env)
-  (lambda (sexp)
-    (match sexp
-      [(? fixnum?) sexp]
-      [(? symbol?) (eval-symbol env sexp)]
-      [`(read) (read-fixnum)]
-      [`(- ,e) (fx- 0 ((interp-exp env) e))]
-      [`(+ ,e1 ,e2) (fx+ ((interp-exp env) e1) ((interp-exp env) e2))]
-      [`(let ([,var ,rexp]) ,body)
-        (let ([value ((interp-exp env) rexp)])
-          ((interp-exp (add-binding env (list var value))) body))])))
-
-(define (read-fixnum)
-  (let ([r (read)])
-    (cond
-       [(fixnum? r) r]
-       [else (error "invalid fixnum in input: " r)])))
-
-(define (env-head-symbol env)
-  (car (car env)))
-
-(define (env-head-value env)
-  (cadr (car env)))
-
-(define (add-binding env binding)
-  (cons binding env))
-    
-(define (eval-symbol env s)
-  (cond
-    [(equal? env `())                 (error "Symbol " s " not found")]
-    [(equal? (env-head-symbol env) s) (env-head-value env)]
-    [else                             (eval-symbol (cdr env) s)]))

rvar.rkt

@@ -0,0 +1,46 @@
+#lang racket
+
+(require racket/fixnum)
+(require racket/dict)
+
+(provide Int Prim Var Let Program interp-RVar-class interp-RVar)
+
+(struct Int (value))
+(struct Var (var))
+(struct Prim (op args))
+(struct Let (var expr body))
+
+(struct Program (info body))
+
+(define interp-RVar-class
+    (class object%
+       (super-new)
+
+       (define/public ((interp-exp env) exp)
+         (match exp
+           [(Int n) n]
+           [(Var v) (eval-symbol env v)]
+           [(Prim 'read '()) (read-fixnum)]
+           [(Prim '- (list e)) (fx- 0 ((interp-exp env) e))]
+           [(Prim '+ `(,e1 ,e2)) (fx+ ((interp-exp env) e1) ((interp-exp env) e2))]
+           [(Let var rexp body)
+            (let ([value ((interp-exp env) rexp)])
+              ((interp-exp (dict-set env var value)) body))]))
+
+       (define/public (interp-program program)
+          (match program
+            [(Program _ body) ((interp-exp (make-immutable-hash)) body)]))))
+
+(define (read-fixnum)
+  (let ([r (read)])
+    (cond
+       [(fixnum? r) r]
+       [else (error "invalid fixnum in input: " r)])))
+
+(define (eval-symbol env s)
+  (if (dict-has-key? env s)
+      (dict-ref env s)
+      (error "Symbol " s " not found")))
+
+(define (interp-RVar program)
+  (send (new interp-RVar-class) interp-program program))

test-c2.rkt

@@ -1,19 +0,0 @@
-#lang racket
-
-(require "test-util.rkt")
-(require "c2.rkt")
-
-(test-eq (env-head-value `((a 1))) 1)
-(test-eq (env-head-symbol `((a 1))) `a)
-(test-eq (eval-symbol `((a 1)) `a) 1)
-(test-eq
-  (let ([env `((a 1) (b 2))])
-    ((interp-exp env) `(+ a (- b))))
-  -1)
-(test-eq
-  ((interp-exp `()) `(let ([a (+ 1 2)]) (+ a 3)))
-  6)
-
-(test-eq
-  ((interp-R1 `()) `(program `() (let ([a (+ 1 2)]) (+ a 3))))
-  6)

test-rvar.rkt

@@ -0,0 +1,39 @@
+#lang racket
+
+(require "test-util.rkt")
+(require "rvar.rkt")
+
+(define (interp-exp env e)
+  ((send (new interp-RVar-class) interp-exp env) e))
+
+(test-eq
+  (let ([env `((a . 1) (b . 2))])
+    (interp-exp env (Var 'a)))
+  1)
+
+(test-eq
+  (let ([env `((a . 1) (b . 2))])
+    (interp-exp env (Prim '+ (list (Var 'a) (Int 3)))))
+  4)
+
+(test-eq
+  (let ([env `((a . 1) (b . 2))])
+    (interp-exp env (Prim '- `(,(Int 3)))))
+  -3)
+
+(test-eq
+  (let ([env `((a . 1) (b . 2))])
+    (interp-exp env (Prim '+ (list (Var 'a) (Prim `- (list (Var 'b)))))))
+  -1)
+
+(test-eq
+  (interp-exp `() (Let 'a
+                       (Prim '+ (list (Int 1) (Int 2)))
+                       (Prim '+ (list (Var 'a) (Int 3)))))
+  6)
+
+(test-eq
+  (interp-RVar (Program `() (Let 'a
+                                 (Prim '+ (list (Int 1) (Int 2)))
+                                 (Prim '+ (list (Var 'a) (Int 3))))))
+  6)