EOPL 第3章の Exercise 3.47

練習問題 3.47 は setdynamic という式を追加して一時的な代入ができるようにする。
Perl の local とか Scala の DynamicVariable に近いかな。

; Exercise 3.47
(load "r5rs.scm")
(load "define-datatype.scm")
(load "sllgen.scm")
(use srfi-1)

; reference

(define-datatype reference reference?
  (a-ref
    (position integer?)
    (vec vector?)))

(define primitive-deref
  (lambda (ref)
    (cases reference ref
      (a-ref (pos vec) (vector-ref vec pos)))))

(define primitive-setref!
  (lambda (ref val)
    (cases reference ref
      (a-ref (pos vec) (vector-set! vec pos val)))))

(define deref
  (lambda (ref)
    (primitive-deref ref)))

(define setref!
  (lambda (ref val)
    (primitive-setref! ref val)))

; boolean

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

; environment

(define-datatype environment environment?
  (empty-env-record)
  (extended-env-record
    (syms (list-of symbol?))
    (vals vector?)
    (env environment?))
  )

(define empty-env
  (lambda ()
    (empty-env-record)))

(define extend-env
  (lambda (syms vals env)
    (extended-env-record syms (list->vector vals) env)))

(define extend-env-recursively
  (lambda (proc-names idss bodies old-env)
    (extended-env-record
      proc-names
      (list->vector
        (map
          (lambda (x) (closure x proc-names idss bodies old-env))
          (iota (length proc-names))))
      old-env)))

(define apply-env
  (lambda (env sym)
    (deref (apply-env-ref env sym))))

(define apply-env-ref
  (lambda (env sym)
    (cases environment env
      (empty-env-record ()
        (eopl:error 'apply-env "No binding for ~s" sym))
      (extended-env-record (syms vals env)
        (let ((pos (list-find-position sym syms)))
          (if (number? pos)
            (a-ref pos vals)
            (apply-env-ref env sym)))))))

(define list-find-position
  (lambda (sym los)
    (list-index (lambda (sym1) (eqv? sym1 sym)) los)))

(define list-index
  (lambda (pred ls)
    (cond
      ((null? ls) #f)
      ((pred (car ls)) 0)
      (else (let ((list-index-r (list-index pred (cdr ls))))
              (if (number? list-index-r)
                (+ list-index-r 1)
                #f))))))

(define-datatype procval procval?
  (closure
    (pos number?)
    (proc-names (list-of symbol?))
    (idss (list-of (list-of symbol?)))
    (bodies (list-of expression?))
    (env environment?)))

(define apply-procval
  (lambda (proc args)
    (cases procval proc
      (closure (pos proc-names idss bodies env)
        (eval-expression
          (list-ref bodies pos)
          (extend-env
            (list-ref idss pos)
            args
            (extend-env-recursively
              proc-names idss bodies env)))))))

(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 0 (list '_) (list ids) (list body) env))
      (app-exp (rator rands)
        (let ((proc (eval-expression rator env))
              (args (eval-rands rands env)))
          (if (procval? proc)
            (apply-procval proc args)
            (eopl:error 'eval-expression
              "Attempt to apply non-procedure ~s" proc))))
      (letrec-exp (proc-names idss bodies letrec-body)
        (eval-expression
          letrec-body
          (extend-env-recursively proc-names idss bodies env)))
      (varassign-exp (id rhs-exp)
        (begin
          (setref!
            (apply-env-ref env id)
            (eval-expression rhs-exp env))
          1))
      ; Excercise 3.47
      (setdynamic-exp (id rhs-exp body)
        (let ((save (apply-env env id)))
          (setref!
            (apply-env-ref env id)
            (eval-expression rhs-exp env))
          (let ((result (eval-expression body env)))
            (setref! (apply-env-ref env id) save)
            result)))
      )))

(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))
      (eq?-prim () (if (eq? (car args) (cadr args)) (true-value) (false-value)))
      )))

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

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

(define grammar-letrec-varassign
  '((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
      ("(" expression (arbno expression) ")")
      app-exp)
    (expression
      ("letrec"
       (arbno
         identifier "(" (separated-list identifier ",") ")" "=" expression)
       "in" expression)
      letrec-exp)
    (expression
      ("set" identifier "=" expression)
      varassign-exp)
    ; Excercise 3.47
    (expression
      ("setdynamic" identifier "=" expression "during" expression)
      setdynamic-exp)
    (primitive ("+") add-prim)
    (primitive ("-") subtract-prim)
    (primitive ("*") mult-prim)
    (primitive ("add1") incr-prim)
    (primitive ("sub1") decr-prim)
    (primitive ("eq?") eq?-prim)
    ))

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

(sllgen:make-define-datatypes scanner-spec-letrec-varassign grammar-letrec-varassign)

(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-letrec-varassign
      grammar-letrec-varassign)))