unsafeCoerce.hs

{-# LANGUAGE StandaloneDeriving, FlexibleContexts, UndecidableInstances #-}
-- Laungh ghci with -fobject-code to make the Fix/Tree trick work (thanks edwardk).

-- courtesy of hpc on #haskell
import Unsafe.Coerce
import Control.Monad.ST

toInteger :: Int -> Integer
isJust :: Maybe a -> Bool
null :: [a] -> Bool
id :: a -> a

toInteger = unsafeCoerce
isJust = unsafeCoerce
null = not . unsafeCoerce
id = unsafeCoerce

newtype Fix f = Fix (f (Fix f))
deriving instance (Show (Fix f), Show (f (Fix f))) => Show (Fix f)

data Tree a = Leaf a | Branch (Tree a) (Tree a)
    deriving (Eq, Ord, Show, Read)

treeToLists :: Tree a -> Fix []
treeToLists = unsafeCoerce

unsafeSTToIO :: ST s a -> IO a
unsafeSTToIO = unsafeCoerce

undefined :: a
undefined = unsafeCoerce unsafeCoerce