Sudoku board

sudoku-board.scm

#lang scheme
; http://www.dailysudoku.com/sudoku/archive/2012/02/2012-02-10.shtml

(define easy-game "020580000093600007001007000609102300180030059005908104000800500200009760000015080")

(define (to-number char)
  (- (char->integer char) 48))

(define (to-vector string)
  (list->vector (map to-number (string->list string))))

(define (cell-value vector line column)
  (let ([val (vector-ref (to-vector easy-game) (+ (* line 9) column))])
    (if (= val 0) "." val)))

(define (display-board game)
  (for ([line (in-range 9)])
    (when (= (modulo line 3) 0) (printf "+-----------+-----------+-----------+\n|"))
    (for ([column (in-range 9)])
      (printf " ~a " (cell-value game line column))
      (if (= (modulo (+ column 1) 3) 0)
          (printf "|")
          (printf " ")))
    (printf "\n")
    (when (= (modulo line 3) 0) (printf "|"))
    (when (= (modulo line 3) 1) (printf "|")))
  (printf "+-----------+-----------+-----------+\n"))

(display-board easy-game)

+-----------+-----------+-----------+
| .   2   . | 5   8   . | .   .   . |
| .   9   3 | 6   .   . | .   .   7 |
| .   .   1 | .   .   7 | .   .   . |
+-----------+-----------+-----------+
| 6   .   9 | 1   .   2 | 3   .   . |
| 1   8   . | .   3   . | .   5   9 |
| .   .   5 | 9   .   8 | 1   .   4 |
+-----------+-----------+-----------+
| .   .   . | 8   .   . | 5   .   . |
| 2   .   . | .   .   9 | 7   6   . |
| .   .   . | .   1   5 | .   8   . |
+-----------+-----------+-----------+

Queria ver a funcao to-chair.