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From: "B. Pym" <No_spamming@noWhere_7073.org>
Newsgroups: comp.lang.lisp
Subject: Re: Searching a character within a line
Date: Sun, 7 Jul 2024 11:43:16 -0000 (UTC)
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Pierre R. Mai wrote:

> (defun get-field-from-line (field line)
>   "Returns a copy of the given field (0 based index) from the line.
> Fields are separated by '|'.  If there are fewer fields in line than
> field, nil is returned."
>   (loop for start = 0 then (1+ position)
>         for position = (and start (position #\| line :start start))
>         repeat field
>         when (null position)
>         do (return nil)
>         finally
>         (return (subseq line start position))))

Gauche Scheme

(use srfi-13) ;; string-take string-index

(define (get-field-of-line index line)
  (let go ((i index) (s line))
    (let ((found (string-index s #\|)))
      (if (zero? i)
        (or (and found (string-take s found)) s)
        (and found (go (- i 1) (string-drop s (+ 1 found))))))))

(get-field-of-line 0 "|2|Dollars|23-dec-1999|Idaho")
  ===>
""

(get-field-of-line 1 "|2|Dollars|23-dec-1999|Idaho")
  ===>
"2"

(get-field-of-line 2 "|2|Dollars|23-dec-1999|Idaho")
  ===>
"Dollars"

(get-field-of-line 3 "|2|Dollars|23-dec-1999|Idaho")
  ===>
"23-dec-1999"

(get-field-of-line 4 "|2|Dollars|23-dec-1999|Idaho")
  ===>
"Idaho"

(get-field-of-line 5 "|2|Dollars|23-dec-1999|Idaho")
  ===>
#f