EOPL 第3章の Exercise 3.29

練習問題 3.29 は proc と同様だけど入口と出口でトレースメッセージを表示する traceproc を追加する。特にどうということはない問題。

; Exercise 3.29
(load "r5rs.scm")
(load "define-datatype.scm")
(load "sllgen.scm")
(load "./2.eopl.scm") ; for extend-env, empty-env

(define true-value (lambda () 1))
(define false-value (lambda () 0))
(define true-value?
  (lambda (x)
    (not (= 0 x))))

(define closure
  (lambda (ids body env)
    (lambda (args)
      (if (= (length ids) (length args))
        (eval-expression body (extend-env ids args env))
        (eopl:error 'closure
                    "Wrong number of arguments: ~s required, but got ~s"
                    (length ids) (length args))))))

(define eval-program
  (lambda (pgm)
    (cases program pgm
      (a-program (body)
        (eval-expression body (init-env))))))

(define eval-expression
  (lambda (exp env)
    (cases expression exp
      (lit-exp (datum) datum)
      (var-exp (id) (apply-env env id))
      (primapp-exp (prim rands)
        (let ((args (eval-rands rands env)))
          (apply-primitive prim args)))
      (if-exp (test-exp true-exp false-exp)
        (if (true-value? (eval-expression test-exp env))
          (eval-expression true-exp env)
          (eval-expression false-exp env)))
      (let-exp (ids rands body)
        (let ((args (eval-rands rands env)))
          (eval-expression body (extend-env ids args env))))
      (proc-exp (ids body)
        (closure ids body env))
      (traceproc-exp (ids body)
        (let ((proc (closure ids body env)))
          (lambda (args)
            (display (format "enter: ~s\n" args))
            (let ((result (proc args)))
              (display (format "exit: ~s\n" result))
              result))))
      (app-exp (rator rands)
        (let ((proc (eval-expression rator env))
              (args (eval-rands rands env)))
          (apply-procval proc args)))
      )))

(define eval-rands
  (lambda (rands env)
    (map (lambda (x) (eval-rand x env)) rands)))

(define eval-rand
  (lambda (rand env)
    (eval-expression rand env)))

(define apply-primitive
  (lambda (prim args)
    (cases primitive prim
      (add-prim () (+ (car args) (cadr args)))
      (subtract-prim () (- (car args) (cadr args)))
      (mult-prim () (* (car args) (cadr args)))
      (incr-prim () (+ (car args) 1))
      (decr-prim () (- (car args) 1))
      )))

(define apply-procval
  (lambda (proc args)
    (proc args)))

(define init-env
  (lambda ()
    (extend-env
      '(i v x)
      '(1 5 10)
      (empty-env))))

(define scanner-spec-3.29
  '((white-sp
      (whitespace) skip)
    (comment
      ("%" (arbno (not #\newline))) skip)
    (identifier
      (letter (arbno (or letter digit "?"))) symbol)
    (number
      (digit (arbno digit)) number)))

(define grammar-3.29
  '((program
      (expression)
      a-program)
    (expression
      (number)
      lit-exp)
    (expression
      (identifier)
      var-exp)
    (expression
      (primitive "(" (separated-list expression ",") ")" )
      primapp-exp)
    (expression
      ("if" expression "then" expression "else" expression)
      if-exp)
    (expression
      ("let" (arbno identifier "=" expression) "in" expression)
      let-exp)
    (expression
      ("proc" "(" (separated-list identifier ",") ")" expression)
      proc-exp)
    (expression
      ("traceproc" "(" (separated-list identifier ",") ")" expression)
      traceproc-exp)
    (expression
      ("(" expression (arbno expression) ")")
      app-exp)
    (primitive ("+") add-prim)
    (primitive ("-") subtract-prim)
    (primitive ("*") mult-prim)
    (primitive ("add1") incr-prim)
    (primitive ("sub1") decr-prim)
    ))

(define scan&parse
  (sllgen:make-string-parser
    scanner-spec-3.29
    grammar-3.29))

(sllgen:make-define-datatypes scanner-spec-3.29 grammar-3.29)

(define run
  (lambda (string)
    (eval-program
      (scan&parse string))))

(define read-eval-print
  (sllgen:make-rep-loop "-->" eval-program
    (sllgen:make-stream-parser
      scanner-spec-3.29
      grammar-3.29)))

; let makemult = traceproc (maker, x)
;                  if x
;                  then +(4, (maker maker -(x, 1)))
;                  else 0
; in let times4 = traceproc (x) (makemult makemult x)
;    in (times4 3)

; -->enter: (3)
; enter: (#<closure (eval-expression eval-expression eval-expression)> 3)
; enter: (#<closure (eval-expression eval-expression eval-expression)> 2)
; enter: (#<closure (eval-expression eval-expression eval-expression)> 1)
; enter: (#<closure (eval-expression eval-expression eval-expression)> 0)
; exit: 0
; exit: 4
; exit: 8
; exit: 12
; exit: 12
; 12