Heuristic Backtracking - Backtracking that prioritizes branches depending on some heuristic

HeuristicBacktrack.hs

module HeuristicBacktrac (backtracking) where
import List

hbacktracking::
     (partialSolution -> partialSolution -> Ordering) -- heuristic, A* like
     -> (partialSolution -> Bool)                     -- isFinalSolution?
     -> (partialSolution -> solution)                 -- convert
     -> (partialSolution -> [partialSolution])        -- next
     -> (partialSolution -> Bool)                     -- isValid?
     -> [partialSolution]                             -- Estado inicial
     -> Maybe solution

hbacktracking _ _ _ _ _ [] = Nothing
hbacktracking order isSolution convert next isValid (ps:pss)
     | isSolution ps = Just (convert ps)
     | otherwise = (hbacktracking order isSolution convert next isValid)
           (sortBy order ((filter isValid (next ps)) ++ pss))

I have some cool pieces of code, specially in haskell, I wrote as an undergraduate. Whenever I find one of them I like to post them here.

I did not test it before posting it, but I guess it works.