{-# LANGUAGE CPP #-}
-- | Compatibility layer for "Data.Semigroup"
module Distribution.Compat.Semigroup
( Semigroup((<>))
, Mon.Monoid(..)
, All(..)
, Any(..)
) where
#if __GLASGOW_HASKELL__ >= 711
-- Data.Semigroup is available since GHC 8.0/base-4.9
import Data.Semigroup
import qualified Data.Monoid as Mon
#else
-- provide internal simplified non-exposed class for older GHCs
import Data.Monoid as Mon (Monoid(..), All(..), Any(..), Dual(..))
class Semigroup a where
(<>) :: a -> a -> a
-- several primitive instances
instance Semigroup () where
_ <> _ = ()
instance Semigroup [a] where
(<>) = (++)
instance Semigroup a => Semigroup (Dual a) where
Dual a <> Dual b = Dual (b <> a)
instance Semigroup a => Semigroup (Maybe a) where
Nothing <> b = b
a <> Nothing = a
Just a <> Just b = Just (a <> b)
instance Semigroup (Either a b) where
Left _ <> b = b
a <> _ = a
instance Semigroup Ordering where
LT <> _ = LT
EQ <> y = y
GT <> _ = GT
instance Semigroup b => Semigroup (a -> b) where
f <> g = \a -> f a <> g a
instance Semigroup All where
All a <> All b = All (a && b)
instance Semigroup Any where
Any a <> Any b = Any (a || b)
instance (Semigroup a, Semigroup b) => Semigroup (a, b) where
(a,b) <> (a',b') = (a<>a',b<>b')
instance (Semigroup a, Semigroup b, Semigroup c)
=> Semigroup (a, b, c) where
(a,b,c) <> (a',b',c') = (a<>a',b<>b',c<>c')
instance (Semigroup a, Semigroup b, Semigroup c, Semigroup d)
=> Semigroup (a, b, c, d) where
(a,b,c,d) <> (a',b',c',d') = (a<>a',b<>b',c<>c',d<>d')
instance (Semigroup a, Semigroup b, Semigroup c, Semigroup d, Semigroup e)
=> Semigroup (a, b, c, d, e) where
(a,b,c,d,e) <> (a',b',c',d',e') = (a<>a',b<>b',c<>c',d<>d',e<>e')
#endif