(define (string-downcase s)
  (let* ((l (string-length s))
         (r (make-string l)))
    (let loop ((i 0))
      (if (eq? i l)
        r
        (begin
          (string-set! r i (char-downcase (string-ref s i)))
          (loop (add1 i)))))))

(define (string-trim-head lst)
  (let loop ((lst lst))
    (if (and (pair? lst) (char=? #\space (car lst)))
      (loop (cdr lst))
      lst)))

(define (string-trim s)
  (list->string
    (reverse
      (string-trim-head
        (reverse
          (string-trim-head
            (string->list s)))))))