Siritori solver in Haskell.

Solver.hs

-- Still under development but I will show you my code.
-- Haskell is beautiful.

import Control.Monad
import Data.List

type Elem = (Int, Int)

-- Either Monad is not defined yet in ghc of 6.x
instance Monad (Either a) where
  Right a >>= f = f a
  Left a >>= _ = Left a
  return = Right

getEither :: Either a a -> a
getEither (Right a) = a
getEither (Left a) = a

-- Generating all the candidate array which is evaluated lazily.
allCombination = f :: [a] -> [[a]]
  where
    g = map permutations . h 
    f = concat . g
    h = filterM (\x -> [True, False]) :: [a] -> [[a]]

-- foldM :: (a->b->m a)->a->[b]->m a
detectChain :: [Elem] -> [Elem]
detectChain = getEither . foldM f [] 
   where
     f [] x = Right [x]
     f ((a,b):xs) (c,d) 
       | b == c = Right $ (c,d):(a,b):xs
       | otherwise = Left $ (a,b):xs

-- returns (the max chain, and its length)
solve :: [Elem] -> [Elem]
solve = undefined

main = do
  content <- getContents
  let elements = read content
  print $ solve elements