sicp/mceval/common.rkt

#lang sicp

(#%require "syntax.rkt")

(#%provide apply-primitive-procedure
           true?
           false?
           prompt-for-input
           announce-output
           user-print
           eval-program)

(define (primitive-implementation proc) (cadr proc))

(define (apply-primitive-procedure proc args)
  (apply
   (primitive-implementation proc) args))

(define (true? x)
  (not (eq? x false)))

(define (false? x)
  (eq? x false))

(define (prompt-for-input string)
  (newline) (newline) (display string) (newline))

(define (announce-output string)
  (newline) (display string) (newline))

(define (user-print object)
  (cond ((compound-procedure? object)
         (display (list 'compound-procedure
                        (procedure-parameters object)
                        (procedure-body object)
                        '<procedure-env>)))
        (else (display object))))

;; Program is a list of expressions to evaluate using the procedure
;; eval.  user-print will be called to print any output.
(define (eval-program program eval user-print env)
  (let loop ((prog program))
    (if (null? (cdr prog))
        (eval (car prog) env)
        (begin
          (eval (car prog) env)
          (loop (cdr prog))))))