Returns the target in replace-list that matches in string at pos See also repl-substring-list?.
(define (repl-substring-list-target string replace-list pos)
;; Return the target that matches in a string
(let loop ((list replace-list))
(let ((target (car list))
(repl (car (cdr list)))
(rest (cdr (cdr list))))
(if (repl-substring? string target pos)
target
(if (null? rest)
#f
(loop rest))))))