Dougal Stanton wrote:
The following is a slap-dash program for generating a list of pairs of words which differ by, at most, one letter. It's quite verbose at the moment, because (a) that was the way I wrote it, a snippet at a time, and (b) I lack the wit to make it shorter.
Can anyone recommend ways to make this program more efficient/neat/elegant? It runs in decent time on my machine, but it's not exceedingly pretty and I'm sure it can be made shorter too.
I like it for its elegant point-free style :)
-- Number of letters difference between two words. difference :: Pair -> Int difference = length . filter (==False) . uncurry (zipWith (==))
Apparently, difference can only detect character replacements but not character insertion or deletion, but that's probably not your use case.
-- Pairs of words of equal length, sorted to reduce -- duplicates of (a,b), (b,a) type. They shouldn't -- be completely eradicated because part of the game -- is to spot when they;re the same word. listPairs :: WordSet -> PairSet listPairs ws = [ (w, w') | w <- ws, w' <- ws, length w == length w', w <= w' ]
You can avoid generating the superfluous half of the pairs by using tails listPairs ws = [ (head ws', w') | ws' <- tails ws, w' <- ws' , let w = head ws', length w == length w'] Of course, grouping words by length first and pairing the resulting groups is more efficient than filtering out all the pairs where length w /= length w'. But you restrict fingerspell to a fixed word length anyway, so it doesn't matter. Regards, apfelmus