Given a string containing delimited tokens, return a list of the tokens in string form.
The string to split.
A list of characters that should be treated as whitespace.
(define (split str #!optional (whitespace '(#\space)))
;; Splits string at whitespace and returns the resulting list of tokens
(let loop ((characters (string->list str)) ; Top-level recursive loop.
(current-word '())
(tokens '()))
; If there are no characters left,
; then we're done!
(cond ((null? characters)
; Is there a token in progress?
(if (null? current-word)
(reverse tokens)
(reverse (cons (list->string (reverse current-word))
tokens))))
; If there are characters left,
; then keep going.
(#t
(let ((c (car characters))
(rest (cdr characters)))
; Are we reading a space?
(cond ((member c whitespace)
(if (null? current-word)
(loop rest '() tokens)
(loop rest
'()
(cons (list->string (reverse current-word))
tokens))))
; We are reading a non-space
(#t
(loop rest (cons c current-word) tokens))))))))