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  1. #lang racket
  2.  
  3. (define (calc-rpn text)
  4.   (let ((table (hash "+" + "-" - "*" * "/" / "%" modulo)))
  5.     (car
  6.      (foldl (lambda (tok stack)
  7.               (when (non-empty-string? tok)
  8.                 (cond ((string->number tok) => (lambda (x)
  9.                                                  (cons x stack)))
  10.                       (else (let ((b (car stack)) (a (cadr stack)))
  11.                               (cons ((hash-ref table tok) a b) (cddr stack)))))))
  12.             '() (string-split text)))))
  13.  
  14. (define (main)
  15.   (printf ">>> ")
  16.   (let ((expr (read-line)))
  17.     (with-handlers ((exn:fail:contract?
  18.                      (lambda (exn)
  19.                        (printf "不正な入力です~%")
  20.                        (main))))
  21.       (unless (char=? (string-ref expr 0) #\q)
  22.         (printf "~a = ~a~%" expr (calc-rpn expr))
  23.         (main)))))
  24.  
  25.  
Success #stdin #stdout 0.66s 89084KB
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https://ideone.com/lJjil8
language:
Racket (racket 7.0)
created:
81 days ago
visibility:
secret

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