Обработка строк

(define (string-trim-left s)
  (define (iter i)
    (if (= i (string-length s))
        ""
        (if (or (char=? (string-ref s i) #\tab) (char=? (string-ref s i) #\space) (char=? (string-ref s i) #\newline))
            (iter (+ i 1))
            (substring s i)))
  )
  (iter 0))

(define (string-trim-right s)
  (define (iter i)
    (if (= i (- 1))
      ""
      (if (or (char=? (string-ref s i) #\tab) (char=? (string-ref s i) #\space) (char=? (string-ref s i) #\newline))
          (iter (- i 1))
          (substring s 0 (+ i 1))))
  )
(iter (- (string-length s) 1)))

(define (string-trim s)
  (string-trim-left (string-trim-right s)))


(define (string-prefix? a b)
  (if (> (string-length a) (string-length b))
      #f
      (string=? (substring b 0 (string-length a)) a)))

(define (string-suffix? a b)
  (if (> (string-length a) (string-length b))
      #f
      (string=? (substring b (- (string-length b) (string-length a))) a)))

(define (string-infix? a b)
  (define (iter a b)
    (if (> (string-length a) (string-length b))
        #f
        (if (string-prefix? a b)
           #t
           (iter a (substring b 1)))))
(iter a b))

(define (string-split str sep)
  (define (iter a b buf)
    (append
      (if (<= (string-length a) (string-length b))
          (if (string-prefix? a b)
              (list buf (iter a (substring b (string-length a)) ""))
              (list (iter a (substring b 1) (string-append buf (substring b 0 1)))))
          (list (string-append buf b))))
  )
  (define (my-flatten l)
    (if (null? l)
        '()
        (append (if (list? (car l))
                    (my-flatten (car l))
                    (list (car l)))
                (if (null? (cdr l))
                    '()
                     (my-flatten (cdr l)))
        ))
    )
   (my-flatten (iter sep str "")))