Coerce.hs

{-# LANGUAGE CPP #-}

#ifndef MIN_VERSION_profunctors
#define MIN_VERSION_profunctors(x,y,z) 0
#endif

#if (MIN_VERSION_profunctors(4,4,0)) && __GLASGOW_HASKELL__ >= 708
#define USE_COERCE
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
#else
{-# LANGUAGE Unsafe #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Copyright   :  (C) 2015 Edward Kmett and Eric Mertens
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
-- This module provides a shim around 'coerce' that defaults to 'unsafeCoerce'
-- on GHC < 7.8
-----------------------------------------------------------------------------
module Control.Lens.Internal.Coerce
  ( coerce
  , coerce'
  ) where

#ifdef USE_COERCE

import Data.Coerce

coerce' :: forall a b. Coercible a b => b -> a
coerce' = coerce (id :: a -> a)
{-# INLINE coerce' #-}

#else

import Unsafe.Coerce

coerce, coerce' :: a -> b
coerce  = unsafeCoerce
coerce' = unsafeCoerce
{-# INLINE coerce #-}
{-# INLINE coerce' #-}
#endif