Merge pull request #50 from endgame/more-instances

MonoidNull: More instances

Author: blamario

CHANGELOG.md

@@ -1,3 +1,26 @@
+Unreleased (Minor)
+------------------
+
+* `Data.Monoid.Null.MonoidNull` now has a default implementation
+* Add instances of `MonoidNull` and (where appropriate) `PositiveMonoid` for:
+  - `(a, b, c, d, e)`
+  - `Data.Functor.Compose f g a`
+  - `Data.Functor.Const r a`
+  - `Data.Functor.Identity a`
+  - `Data.Functor.Product f g a`
+  - `Data.Ord.Down a`
+  - `Data.Proxy.Proxy a`
+  - `Data.Semigroup.Max a`
+  - `Data.Semigroup.Min a`
+  - `Data.Semigroup.WrappedMonoid a`
+  - `GHC.Generics.(:*:) f g a`
+  - `GHC.Generics.(:.:) f g a`
+  - `GHC.Generics.K1 i c p`
+  - `GHC.Generics.M1 i c f p`
+  - `GHC.Generics.Par1 p`
+  - `GHC.Generics.Rec1 f p`
+  - `GHC.Generics.U1 p`
+
 Version 1.2.4.1
 ---------------
 * Bumped the `text` dependency upper bounds

src/Data/Monoid/Null.hs

@@ -1,20 +1,27 @@
-{- 
+{-
     Copyright 2013-2015 Mario Blazevic
 
     License: BSD3 (see BSD3-LICENSE.txt file)
 -}
 
 -- | This module defines the MonoidNull class and some of its instances.
--- 
+--
 
-{-# LANGUAGE Haskell2010, FlexibleInstances, Trustworthy #-}
+{-# LANGUAGE Haskell2010, CPP, FlexibleInstances, DefaultSignatures, Trustworthy #-}
 
 module Data.Monoid.Null (
    MonoidNull(..), PositiveMonoid
    )
 where
-   
+
+import Data.Functor.Compose (Compose(..))
+import Data.Functor.Const (Const(..))
+import Data.Functor.Identity (Identity(..))
 import Data.Monoid -- (Monoid, First(..), Last(..), Dual(..), Sum(..), Product(..), All(getAll), Any(getAny))
+import Data.Ord (Down(..))
+import Data.Proxy (Proxy)
+import Data.Semigroup (Max, Min, WrappedMonoid(..))
+import qualified Data.Functor.Product as Functor
 import qualified Data.List as List
 import qualified Data.ByteString as ByteString
 import qualified Data.ByteString.Lazy as LazyByteString
@@ -26,21 +33,24 @@ import qualified Data.Map as Map
 import qualified Data.Sequence as Sequence
 import qualified Data.Set as Set
 import qualified Data.Vector as Vector
+import GHC.Generics ((:*:)(..), (:.:)(..), K1(..), M1(..), Par1(..), Rec1(..), U1)
 import Numeric.Natural (Natural)
 
 import Prelude hiding (null)
 
 -- | Extension of 'Monoid' that allows testing a value for equality with 'mempty'. The following law must hold:
--- 
+--
 -- prop> null x == (x == mempty)
--- 
+--
 -- Furthermore, the performance of this method should be constant, /i.e./, independent of the length of its argument.
 class Monoid m => MonoidNull m where
    null :: m -> Bool
+   default null :: Eq m => m -> Bool
+   null = (==) mempty
 
 -- | Subclass of 'Monoid' for types whose values have no inverse, with the exception of 'Data.Monoid.mempty'. More
 -- formally, the class instances must satisfy the following law:
--- 
+--
 -- prop> null (x <> y) == (null x && null y)
 class MonoidNull m => PositiveMonoid m
 
@@ -73,10 +83,78 @@ instance (Num a, Eq a) => MonoidNull (Sum a) where
 instance (Num a, Eq a) => MonoidNull (Product a) where
    null (Product a) = a == 1
 
+-- | @since 1.2.5.0
+instance (Ord a, Bounded a) => MonoidNull (Max a)
+
+-- | @since 1.2.5.0
+instance (Ord a, Bounded a) => MonoidNull (Min a)
+
 instance Monoid a => MonoidNull (Maybe a) where
    null Nothing = True
    null _ = False
 
+#if MIN_VERSION_base(4, 11, 0)
+-- | @since 1.2.5.0
+instance MonoidNull a => MonoidNull (Down a) where
+   null (Down a) = null a
+#endif
+
+#if MIN_VERSION_base(4, 12, 0)
+-- | @since 1.2.5.0
+instance MonoidNull c => MonoidNull (K1 i c p) where
+   null (K1 c) = null c
+
+-- | @since 1.2.5.0
+instance MonoidNull (f p) => MonoidNull (M1 i c f p) where
+   null (M1 fp) = null fp
+
+-- | @since 1.2.5.0
+instance MonoidNull p => MonoidNull (Par1 p) where
+   null (Par1 p) = null p
+
+-- | @since 1.2.5.0
+instance MonoidNull (f p) => MonoidNull (Rec1 f p) where
+   null (Rec1 fp) = null fp
+
+-- | @since 1.2.5.0
+instance MonoidNull (U1 p) where
+   null _ = True
+
+-- | @since 1.2.5.0
+instance (MonoidNull (f p), MonoidNull (g p)) => MonoidNull ((:*:) f g p) where
+   null (fp :*: gp) = null fp && null gp
+
+-- | @since 1.2.5.0
+instance (MonoidNull (f (g p))) => MonoidNull ((:.:) f g p) where
+   null (Comp1 fgp) = null fgp
+#endif
+
+#if MIN_VERSION_base(4, 16, 0)
+-- | @since 1.2.5.0
+instance MonoidNull (f (g a)) => MonoidNull (Compose f g a) where
+   null (Compose fga) = null fga
+
+-- | @since 1.2.5.0
+instance (MonoidNull (f a), MonoidNull (g a)) => MonoidNull (Functor.Product f g a) where
+   null (Functor.Pair fa ga) = null fa && null ga
+#endif
+
+-- | @since 1.2.5.0
+instance MonoidNull r => MonoidNull (Const r a) where
+   null (Const r) = null r
+
+-- | @since 1.2.5.0
+instance MonoidNull a => MonoidNull (Identity a) where
+   null (Identity a) = null a
+
+-- | @since 1.2.5.0
+instance MonoidNull a => MonoidNull (WrappedMonoid a) where
+   null (WrapMonoid a) = null a
+
+-- | @since 1.2.5.0
+instance MonoidNull (Proxy a) where
+   null _ = True
+
 instance (MonoidNull a, MonoidNull b) => MonoidNull (a, b) where
    null (a, b) = null a && null b
 
@@ -86,6 +164,10 @@ instance (MonoidNull a, MonoidNull b, MonoidNull c) => MonoidNull (a, b, c) wher
 instance (MonoidNull a, MonoidNull b, MonoidNull c, MonoidNull d) => MonoidNull (a, b, c, d) where
    null (a, b, c, d) = null a && null b && null c && null d
 
+-- | @since 1.2.5.0
+instance (MonoidNull a, MonoidNull b, MonoidNull c, MonoidNull d, MonoidNull e) => MonoidNull (a, b, c, d, e) where
+   null (a, b, c, d, e) = null a && null b && null c && null d && null e
+
 instance MonoidNull [x] where
    null = List.null
 
@@ -133,6 +215,10 @@ instance PositiveMonoid Text.Text
 instance PositiveMonoid LazyText.Text
 instance PositiveMonoid (Product Natural)
 instance PositiveMonoid (Sum Natural)
+-- | @since 1.2.5.0
+instance (Ord a, Bounded a) => PositiveMonoid (Min a)
+-- | @since 1.2.5.0
+instance (Ord a, Bounded a) => PositiveMonoid (Max a)
 instance Monoid a => PositiveMonoid (Maybe a)
 instance PositiveMonoid (First a)
 instance PositiveMonoid (Last a)
@@ -144,6 +230,39 @@ instance PositiveMonoid IntSet.IntSet
 instance PositiveMonoid (Sequence.Seq a)
 instance Ord a => PositiveMonoid (Set.Set a)
 instance PositiveMonoid (Vector.Vector a)
+-- | @since 1.2.5.0
+instance PositiveMonoid r => PositiveMonoid (Const r a)
+-- | @since 1.2.5.0
+instance PositiveMonoid a => PositiveMonoid (Identity a)
+-- | @since 1.2.5.0
+instance PositiveMonoid a => PositiveMonoid (WrappedMonoid a)
+-- | @since 1.2.5.0
+instance PositiveMonoid (Proxy a)
+
+#if MIN_VERSION_base(4, 11, 0)
+-- | @since 1.2.5.0
+instance PositiveMonoid a => PositiveMonoid (Down a)
+#endif
+
+#if MIN_VERSION_base(4, 12, 0)
+-- | @since 1.2.5.0
+instance PositiveMonoid c => PositiveMonoid (K1 i c p)
+-- | @since 1.2.5.0
+instance PositiveMonoid (f p) => PositiveMonoid (M1 i c f p)
+-- | @since 1.2.5.0
+instance PositiveMonoid p => PositiveMonoid (Par1 p)
+-- | @since 1.2.5.0
+instance PositiveMonoid (f p) => PositiveMonoid (Rec1 f p)
+-- | @since 1.2.5.0
+instance PositiveMonoid (U1 p)
+-- | @since 1.2.5.0
+instance (PositiveMonoid (f (g p))) => PositiveMonoid ((:.:) f g p)
+#endif
+
+#if MIN_VERSION_base(4, 16, 0)
+-- | @since 1.2.5.0
+instance PositiveMonoid (f (g a)) => PositiveMonoid (Compose f g a)
+#endif
 
 -- The possible tuple instances would be overlapping, so we leave the choice to the user.
 --