There is a mistake in your example, I've copied below a working one.
(renamed variable P to ph)
I think racket has excellent documentation. There seems to be a very
fine line between overly verbose documentation and concise
documentation.
Horace.
#lang slideshow
;; Digit = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
;; NL = number or list = Digit | (list of Digits)
;; Sudoku = (list of list of NL)
(define (digit->char i)
(integer->char (+ 48 i)))
(define (Build-list n f) (build-list n (lambda (i) (f (add1 i)))))
;; print-sudoku: Sudoku -> Pict
;; to build a picture of a sudoku as a 9x9 table, with all 9 boxes
boxed, with a text picture for each big number, and a 3x3 table of
text pictures for each empty cell list.
(define (print-sudoku S)
(define (NL->pict nl)
(if (list? nl)
(table 3 (Build-list 9 (lambda (i)
(if (member i nl)
(text (make-string 1 (digit->char i))
"Courier" 16 0)
(text " " "Courier" 16 0))))
(cons cc-superimpose cc-superimpose)
(cons cc-superimpose cc-superimpose)
(cons 0 0) (cons 0 0))
(inset (t (list->string (list (digit->char nl)))) 20 0)))
(let* ([unboxed-table (table 9 (map NL->pict (apply append S))
(cons cc-superimpose cc-superimpose)
(cons cc-superimpose cc-superimpose)
(cons 0 0) (cons 10 10))]
[pw (pict-width unboxed-table)]
[ph (pict-height unboxed-table)]
[thick-box-lines
(linewidth 7 (lt-superimpose
(rectangle pw ph)
(rectangle (/ pw 3) ph) (rectangle (* 2 (/ pw 3)) ph)
(rectangle pw (/ ph 3)) (rectangle pw (* 2 (/ ph 3)))))])
(lt-superimpose
unboxed-table thick-box-lines
(rectangle (* pw (/ 1 9)) ph) (rectangle pw (* ph (/ 1 9)))
(rectangle (* pw (/ 2 9)) ph) (rectangle pw (* ph (/ 2 9)))
(rectangle (* pw (/ 3 9)) ph) (rectangle pw (* ph (/ 3 9)))
(rectangle (* pw (/ 4 9)) ph) (rectangle pw (* ph (/ 4 9)))
(rectangle (* pw (/ 5 9)) ph) (rectangle pw (* ph (/ 5 9)))
(rectangle (* pw (/ 6 9)) ph) (rectangle pw (* ph (/ 6 9)))
(rectangle (* pw (/ 7 9)) ph) (rectangle pw (* ph (/ 7 9)))
(rectangle (* pw (/ 8 9)) ph) (rectangle pw (* ph (/ 8 9))))))
(define Unsolvable#7
'((8 (3 7) (3 5 7) 2 (3 5) 1 9 4 6)
(2 4 6 (7 8) 9 (5 7 8) (5 7) 1 3)
((3 5) 1 9 (3 7) 4 6 (5 7) 8 2)
(1 2 4 (3 6 8) (3 8) (5 7) (3 6) (5 7) 9)
((3 5 7) (3 6 7) 8 9 2 4 (3 6) (5 7) 1)
(9 (3 6 7) (5 7) (1 6 7) (1 3 5 6) (3 7) 8 2 4)
((3 6 7) 5 (2 3 7) 4 (3 6) (2 3) 1 9 8)
(4 8 (1 3) (1 3 6) 7 9 2 (3 6) 5)
((3 6) 9 (1 2) 5 (1 8) (2 8) 4 (3 6) 7)))
(print-sudoku Unsolvable#7)
_________________________________________________
For list-related administrative tasks:
http://lists.racket-lang.org/listinfo/users
