#lang racket
(define (tokenize s)
(let loop ([i 0]
[tok ""]
[result '()])
(if (< i (string-length s))
(let ([c (substring s i (+ 1 i))])
(cond [(regexp-match #rx"[ \t\r\n]" c)
(loop (+ 1 i) "" (append result
(if (> (string-length tok) 0)
(list tok)
'())))]
[(regexp-match #rx"[()]" c)
(loop (+ 1 i) ""
(if (> (string-length tok) 0)
(append result (list tok c))
(append result (list c))))]
[else
(loop (+ 1 i) (string-append tok c) result)]))
(if (> (string-length tok) 0)
(append result (list tok))
result))))
(define-syntax-rule (++ x)
(set! x (+ 1 x)))
(define (process-tokens lst)
(define pos 0)
(define (proc accum)
;(displayln (list "pos" pos))
(if (< pos (length lst))
(begin
(let ([t (list-ref lst pos)])
(++ pos)
(cond [(string=? t "(") (proc (append accum (list (proc '()))))]
[(string=? t ")") accum]
[else (proc (append accum (list t)))]))
)
accum))
(proc '()))
(define (parse-list s)
(let ([tokens (tokenize s)])
(process-tokens tokens)))
(define (main)
(define test "(a b call (d e) foo)")
(for ([x (tokenize test)]) (displayln x))
(define r (parse-list test))
(displayln r)
(for ([x r]) (displayln x)))
(main)