-- FlexibleInstances is needed for OverlappingInstances to be used
-- meaningfully.
{-# LANGUAGE CPP
           , ForeignFunctionInterface
           , OverlappingInstances
           , FlexibleInstances
           #-}

----------------------------------------------------------------
--                                                  ~ 2009.03.17
-- |
-- Module      :  Cabal.FFIHugsTest
-- Copyright   :  Copyright (c) 2009 wren ng thornton
-- License     :  BSD3
-- Maintainer  :  wren@community.haskell.org
-- Stability   :  provisional
-- Portability :  semi-portable (CPP, FFI, OverlappingInstances)
--
-- This package is a minimal regression suite for debugging Cabal's
-- interaction with ffihugs when building for Hugs. This suite fails
-- under Cabal-1.2.3.0 with Hugs-September2006, and is believed to
-- fail under Cabal 1.6 as well. There are two distinct bugs, see
-- the README file for more details.
--
--    * <http://hackage.haskell.org/trac/hackage/ticket/526>
--
--    * <http://hackage.haskell.org/trac/hackage/ticket/527>
----------------------------------------------------------------
module Cabal.FFIHugsTest
    ( Class(..)
    , logarithm
    ) where


-- | Requires OverlappingInstances and FlexibleInstances. Thus, +o
-- and -98 (respectively) should be used in both hugs and ffihugs.
class Class a where
    classy :: a -> a

-- For debugging the debugging
instance Class Bool where
    classy = const False

-- For making the next two really overlap
instance Class Int where
    classy = const 1

instance Class a => Class (Maybe a) where
    classy (Just a) = Just (classy a)
    classy Nothing  = Nothing

instance Class (Maybe Int) where
    classy (Just _) = Just 0
    classy Nothing  = Nothing


-- | Requires CPP and FFI. Thus cpp/cpphs should be run before
-- ffihugs.
#ifdef __USE_FFI__
foreign import ccall unsafe "math.h log"
    logarithm :: Double -> Double
#else
logarithm :: Double -> Double
logarithm = log
#endif


-- | This is just for debugging that Cabal's -D__HUGS__ doesn't
-- override our own -D__HUGS__=200609. (Which is correct in
-- Cabal-1.2.3.0.)
hugsVersion :: String
#if defined(__HUGS__)
#    if __HUGS__ > 0
hugsVersion = "Greater than 0"
#    else
hugsVersion = "Is 0"
#    endif
#else
hugsVersion = "Not Hugs"
#endif