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

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