june 2016 contest code - performance improved

import Data.List
import Data.Int
import Data.Bits
import System.IO

type Bitmap = Int64
data Problem = Problem Int {-rows-} Int {-cols-} Bitmap {-board-} [Bitmap] {-tiles-}
  
extract :: [String] -> [Problem]
extract ls =
  let groups c = takeWhile (not . null) . unfoldr (Just . break ((== c) . last)
                                                     . dropPatt) where
        dropPatt (s:tl)| c == last s = tl
        dropPatt x = x
      texts = groups '=' ls in
   map (single . groups ':') texts where
     single :: [[[Char]]] -> Problem
     single (board:tiles) =
       let m = length board; n = length (head board)
           toBitmap charss = foldr1 (.|.) [if c =='1' then bit (i*n+j) else 0|
                                           (row, i) <- zip charss [0..],
                                           (c, j) <- zip row [0..]] in
       Problem m n (toBitmap board) (map toBitmap tiles)

solve :: Problem -> [(Int, Int)]
solve (Problem m n board tiles) =
  let combine tile run =
        [(curr .|. shifted, (i,j):coords)| (curr, coords) <- run,
         i <- [0..m-1], j <- [0..n-1], let shifted = shiftL tile (i*n+j),
         shifted .&. board == shifted && shifted .&. curr == 0]
      varz = foldr combine [(0,[])] tiles
      Just (_,coords) = find ((==) board . fst) varz in
  coords

main = do
  f <- openFile "./input.dat" ReadMode
  problems <- fmap (extract . filter (not . null) . lines) $ hGetContents f
  putStrLn . unlines . map (intercalate ", " . map show . solve) $ problems