regex - how to parse this string in scheme? -

i have string looks this

"21 4\n21 2 _ _ 19 11\n 12 _ _ 1 _ _\n_ _ _ 7 13 _" 

(there blank space between 21 , 4, 21 , 2, 2 , _, etc)

i loop through it, extract each number, character _ or \n.

(basically split string on blank spaces , on \n)

using substring not work because elements have more 1 character (like 21 or 13)

if easiest way convert string list like

["21" "4" "\n" "21" "2" "_" "_" "19" "11" "\n"...] 

that fine not sure how it.

here started. not use regular expressions - repeated use of read.

#lang racket  (define (parse-line line)   (define in (open-input-string line))   (for/list ([sym (in-port read in)])     (~a sym)))  (define (parse str)   (define in (open-input-string str))   (for/list ([line (in-lines in)])     (parse-line line)))   (parse "21 4\n21 2 _ _ 19 11\n 12 _ _ 1 _ _\n_ _ _ 7 13 _") 

the output is:

'(("21" "4")    ("21" "2" "_" "_" "19" "11")    ("12" "_" "_" "1" "_" "_")    ("_" "_" "_" "7" "13" "_"))