cl:string-chunk   scheme

; (cl:string-chunk "M 3.4, Central California" "M" ",")
(define cl:string-chunk
   (lambda (z char_left char_right)
      (if (or (> (string-length char_left) 1) (> (string-length char_right) 1))
          (print "can't use matching strings longer than 1 char")
          (let ((left_half (cl:string-split z char_left 'right)))
             (if left_half
                 (cl:string-split left_half char_right 'left)
                 #f)))))