From a quick glance it looks to only check conflicts at the box level, not row and column. This is the first CoffeeScript I've seen, it's nice and concise.
Thanks for clarifying. If you've the time, could you tell me how I should read:
non_conflicting = (g) -> ![0...9].some (i) -> g in [s[x][i], s[i][y], box i]
[0...9].some (i) -> g in [s[x][i], s[i][y], box i]
returns true iff it finds some i in [0,9) such that given a guess g, g equals either s[x][i] or s[i][y] or box i or in other words it finds a conflict in either a row or column or box for g assuming it g is at s[x][y]
The ! at the start negates it - so the whole method non_conflicting returns true iff g does not conflict with any i.
If Arrays in JavaScript had an "all" reducer it could be written like this:
non_conflicting = (g) -> [0...9].all (i) -> g not in [s[x][i], s[i][y], box i]
