To build:

$ cabal configure
$ cabal build

To run tests:
$ ./runtests

This sudoku solver takes a single command-line argument, specifying the name
of a file with a sudoku puzzle in it. The first 9x9 = 81 digit characters of
this puzzle file will be used to fill in the internal puzzle array row-by-row.
So, a sensible human-and-machine-readable format might look like:

000003017
015009008
060000000
100007000
009000200
000500004
000000020
500600340
340200000

The zero digit denotes an empty square. Upon completion, the program will
either print a message noting that there was no solution, or it will print
out the solved puzzle in the above format.