連続する数列をハイフンでまとめるSchemeスクリプト

久しぶりの Scheme。約5ヶ月ぶり。ネタも古くてこれ。

　cf. 連続する数列をハイフンでまとめるPythonスクリプト – blog.PanicBlanket.com

(define f
  (lambda (p)
    (cond
      ((= (cadr p) 1) "")
      ((> (cadr p) 1) (string-append (number->string (car p)) ", ")))))

(define g
  (lambda (p)
    (cond
      ((= (cadr p) 1) (string-append (number->string (car p)) "-"))
      ((> (cadr p) 1) (string-append (number->string (car p)) ", ")))))

(define serial
  (lambda (s l)
    (let ((p (car l)))
      (cond
        ((= (cadr p) 1) (serial (string-append s (f p)) (cdr l)))
        ((> (cadr p) 1) (discrete (string-append s (f p)) (cdr l)))
        (else (string-append s (number->string (car p))))))))

(define discrete
  (lambda (s l)
    (let ((p (car l)))
      (cond
        ((= (cadr p) 1) (serial (string-append s (g p)) (cdr l)))
        ((> (cadr p) 1) (discrete (string-append s (g p)) (cdr l)))
        (else (string-append s (number->string (car p))))))))

(define list-with-diff
  (lambda (lis)
    (map list lis (append (map - (cdr lis) lis) (list 0)))))

(define hyphenate
  (lambda (str)
    (letrec ((lis (map string->number (string-split str " ")))
             (l (list-with-diff lis)))
      (cond
        ((= (cadar l) 1) (serial (g (car l)) (cdr l)))
        (else (discrete (g (car l)) (cdr l)))))))

(print (hyphenate "1 2 3"))
(print (hyphenate "1 2 3 5 7 8"))
(print (hyphenate "1 3 4 5 7"))

takatoh@nightschool $ gosh hyphenate_num.scm
1-3
1-3, 5, 7-8
1, 3-5, 7