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  1. #!/usr/bin/env racket
  2.  
  3. #lang racket
  4.  
  5. (require srfi/48)
  6.  
  7. (define *table* (hasheq '+ + '- - '* * '/ /))
  8.  
  9. (define (rpn exp)
  10.   (let loop ((tokens (string-split exp)) (stack '()))
  11.     (if (null? tokens)
  12.         (car stack)
  13.         (let ((token (car tokens)))
  14.           (let ((num (string->number token)))
  15.             (loop (cdr tokens)
  16.                   (cons
  17.                    (or num (apply (hash-ref *table* (string->symbol token))
  18.                                   (reverse (take stack 2))))
  19.                    ((lambda (x)
  20.                       (if num
  21.                           x
  22.                           (drop x 2))) stack))))))))
  23.  
  24. (define (repl arg)
  25.   (display "rpn > ")
  26.   (with-handlers ((exn:fail?
  27.                    (lambda (v)
  28.                      (display "不正な入力です\n")
  29.                      (repl #f))))
  30.     (repl 
  31.      (display
  32.       (format "~1,4F~%" (let ((exp (read-line)))
  33.                           (if (string=? exp "quit")
  34.                               (exit)
  35.                               (rpn exp))))))))
  36.  
  37. (repl #f)
Success #stdin #stdout 0.57s 91052KB
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6.1 5.2 4.3 * + 3.4 2.5 / 1.6 * -
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Standard output is empty
https://ideone.com/EA2a8Q
language:
Racket (racket 7.0)
created:
2 years ago
visibility:
public

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