{-# LANGUAGE ExistentialQuantification, Rank2Types #-}

module Util(

forceList,

gzip, universeParentBi,

exitMessage, exitMessageImpure,

getContentsUTF8

) where

import System.Exit

import System.IO

import System.IO.Unsafe

import Unsafe.Coerce

import Data.Data

import Data.Generics.Uniplate.DataOnly

forceList :: [a] -> [a]

forceList xs = length xs `seq` xs

exitMessage :: String -> IO a

exitMessage msg = do

hPutStrLn stderr msg

exitWith $ ExitFailure 1

exitMessageImpure :: String -> a

exitMessageImpure = unsafePerformIO . exitMessage

getContentsUTF8 :: IO String

getContentsUTF8 = do

hSetEncoding stdin utf8

getContents

data Box = forall a . Data a => Box a

gzip :: Data a => (forall b . Data b => b -> b -> c) -> a -> a -> Maybe [c]

gzip f x y | toConstr x /= toConstr y = Nothing

| otherwise = Just $ zipWith op (gmapQ Box x) (gmapQ Box y)

-- unsafeCoerce is safe because gmapQ on the same constr gives the same fields

-- in the same order

where op (Box x) (Box y) = f x (unsafeCoerce y)

universeParent :: Data a => a -> [(Maybe a, a)]

universeParent x = (Nothing,x) : f x

where

f :: Data a => a -> [(Maybe a, a)]

f x = concat [(Just x, y) : f y | y <- children x]

universeParentBi :: (Data a, Data b) => a -> [(Maybe b, b)]

universeParentBi = concatMap universeParent . childrenBi