{-# LANGUAGE CPP #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}
#if __GLASGOW_HASKELL__ >= 704
{-# LANGUAGE Safe #-}
#else
{-# LANGUAGE Trustworthy #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Semigroup.Generic
-- Copyright   :  (C) 2014-2015 Edward Kmett, Eric Mertens
-- License     :  BSD-style (see the file LICENSE)
--
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  provisional
-- Portability :  portable
--
-- This module provides generic deriving tools for monoids and semigroups for
-- product-like structures.
--
----------------------------------------------------------------------------
module Data.Semigroup.Generic
  ( -- * Generic method implementations
    gmappend, gmempty

    -- * Adapter newtype
  , GenericSemigroupMonoid(..)

    -- * Internal classes
  , GSemigroup, GMonoid
  ) where

#if !(MIN_VERSION_base(4,8,0))
import Data.Monoid (Monoid(..))
#endif
#if !(MIN_VERSION_base(4,11,0))
import Data.Semigroup (Semigroup(..))
#endif
import GHC.Generics

-- | Generically generate a 'Semigroup' ('<>') operation for any type
-- implementing 'Generic'. This operation will append two values
-- by point-wise appending their component fields. It is only defined
-- for product types.
--
-- @
-- 'gmappend' a ('gmappend' b c) = 'gmappend' ('gmappend' a b) c
-- @
gmappend :: (Generic a, GSemigroup (Rep a)) => a -> a -> a
gmappend :: a -> a -> a
gmappend a
x a
y = Rep a Any -> a
forall a x. Generic a => Rep a x -> a
to (Rep a Any -> Rep a Any -> Rep a Any
forall (f :: * -> *) p. GSemigroup f => f p -> f p -> f p
gmappend' (a -> Rep a Any
forall a x. Generic a => a -> Rep a x
from a
x) (a -> Rep a Any
forall a x. Generic a => a -> Rep a x
from a
y))

class GSemigroup f where
  gmappend' :: f p -> f p -> f p

instance GSemigroup U1 where
  gmappend' :: U1 p -> U1 p -> U1 p
gmappend' U1 p
_ U1 p
_ = U1 p
forall k (p :: k). U1 p
U1

instance GSemigroup V1 where
  gmappend' :: V1 p -> V1 p -> V1 p
gmappend' V1 p
x V1 p
y = V1 p
x V1 p -> V1 p -> V1 p
`seq` V1 p
y V1 p -> V1 p -> V1 p
`seq` [Char] -> V1 p
forall a. HasCallStack => [Char] -> a
error [Char]
"GSemigroup.V1: gmappend'"

instance Semigroup a => GSemigroup (K1 i a) where
  gmappend' :: K1 i a p -> K1 i a p -> K1 i a p
gmappend' (K1 a
x) (K1 a
y) = a -> K1 i a p
forall k i c (p :: k). c -> K1 i c p
K1 (a
x a -> a -> a
forall a. Semigroup a => a -> a -> a
<> a
y)

instance GSemigroup f => GSemigroup (M1 i c f) where
  gmappend' :: M1 i c f p -> M1 i c f p -> M1 i c f p
gmappend' (M1 f p
x) (M1 f p
y) = f p -> M1 i c f p
forall k i (c :: Meta) (f :: k -> *) (p :: k). f p -> M1 i c f p
M1 (f p -> f p -> f p
forall (f :: * -> *) p. GSemigroup f => f p -> f p -> f p
gmappend' f p
x f p
y)

instance (GSemigroup f, GSemigroup g) => GSemigroup (f :*: g) where
  gmappend' :: (:*:) f g p -> (:*:) f g p -> (:*:) f g p
gmappend' (f p
x1 :*: g p
x2) (f p
y1 :*: g p
y2) = f p -> f p -> f p
forall (f :: * -> *) p. GSemigroup f => f p -> f p -> f p
gmappend' f p
x1 f p
y1 f p -> g p -> (:*:) f g p
forall k (f :: k -> *) (g :: k -> *) (p :: k).
f p -> g p -> (:*:) f g p
:*: g p -> g p -> g p
forall (f :: * -> *) p. GSemigroup f => f p -> f p -> f p
gmappend' g p
x2 g p
y2

-- | Generically generate a 'Monoid' 'mempty' for any product-like type
-- implementing 'Generic'.
--
-- It is only defined for product types.
--
-- @
-- 'gmappend' 'gmempty' a = a = 'gmappend' a 'gmempty'
-- @

gmempty :: (Generic a, GMonoid (Rep a)) => a
gmempty :: a
gmempty = Rep a Any -> a
forall a x. Generic a => Rep a x -> a
to Rep a Any
forall (f :: * -> *) p. GMonoid f => f p
gmempty'

class GSemigroup f => GMonoid f where
  gmempty' :: f p

instance GMonoid U1 where
  gmempty' :: U1 p
gmempty' = U1 p
forall k (p :: k). U1 p
U1

instance (Semigroup a, Monoid a) => GMonoid (K1 i a) where
  gmempty' :: K1 i a p
gmempty' = a -> K1 i a p
forall k i c (p :: k). c -> K1 i c p
K1 a
forall a. Monoid a => a
mempty

instance GMonoid f => GMonoid (M1 i c f) where
  gmempty' :: M1 i c f p
gmempty' = f p -> M1 i c f p
forall k i (c :: Meta) (f :: k -> *) (p :: k). f p -> M1 i c f p
M1 f p
forall (f :: * -> *) p. GMonoid f => f p
gmempty'

instance (GMonoid f, GMonoid g) => GMonoid (f :*: g) where
  gmempty' :: (:*:) f g p
gmempty' = f p
forall (f :: * -> *) p. GMonoid f => f p
gmempty' f p -> g p -> (:*:) f g p
forall k (f :: k -> *) (g :: k -> *) (p :: k).
f p -> g p -> (:*:) f g p
:*: g p
forall (f :: * -> *) p. GMonoid f => f p
gmempty'

-- | An adapter newtype, suitable for @DerivingVia@. Its 'Semigroup' and
-- 'Monoid' instances leverage the 'Generic'-based defaults defined by
-- 'gmappend' and 'gmempty'. Here is an example of how to use it:
--
-- @
-- &#123;-&#35; LANGUAGE DerivingVia &#35;-&#125;
-- import "Data.Semigroup.Generic"
--
-- data Pair a = MkPair a a
--   deriving ('Semigroup', 'Monoid') via ('GenericSemigroupMonoid' (Pair a))
-- @
newtype GenericSemigroupMonoid a =
  GenericSemigroupMonoid { GenericSemigroupMonoid a -> a
getGenericSemigroupMonoid :: a }

instance (Generic a, GSemigroup (Rep a)) => Semigroup (GenericSemigroupMonoid a) where
  GenericSemigroupMonoid a
x <> :: GenericSemigroupMonoid a
-> GenericSemigroupMonoid a -> GenericSemigroupMonoid a
<> GenericSemigroupMonoid a
y =
    a -> GenericSemigroupMonoid a
forall a. a -> GenericSemigroupMonoid a
GenericSemigroupMonoid (a -> a -> a
forall a. (Generic a, GSemigroup (Rep a)) => a -> a -> a
gmappend a
x a
y)
instance (Generic a, GMonoid (Rep a)) => Monoid (GenericSemigroupMonoid a) where
  mempty :: GenericSemigroupMonoid a
mempty = a -> GenericSemigroupMonoid a
forall a. a -> GenericSemigroupMonoid a
GenericSemigroupMonoid a
forall a. (Generic a, GMonoid (Rep a)) => a
gmempty
#if !(MIN_VERSION_base(4,11,0))
  mappend = (<>)
#endif