generic-deriving-1.12.2: Generic programming library for generalised deriving.

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Generics.Deriving.Monoid

Contents

Description

This module provides two main features:

  1. GMonoid, a generic version of the Monoid type class, including instances of the types from Data.Monoid
  2. Default generic definitions for the Monoid methods mempty and mappend

The generic defaults only work for types without alternatives (i.e. they have only one constructor). We cannot in general know how to deal with different constructors.

Synopsis

GMonoid type class

class GMonoid a where

Methods

gmempty :: a

Generic mempty

gmappend :: a -> a -> a

Generic mappend

gmconcat :: [a] -> a

Generic mconcat

Instances

GMonoid Ordering 
GMonoid () 
GMonoid Any 
GMonoid All 
GMonoid [a] 
GMonoid a => GMonoid (Maybe a) 
Num a => GMonoid (Sum a) 
Num a => GMonoid (Product a) 
GMonoid (Endo a) 
GMonoid a => GMonoid (Dual a) 
GMonoid (Last a) 
GMonoid (First a) 
GMonoid a => GMonoid (Down a) 
GMonoid b => GMonoid (a -> b) 
(GMonoid a, GMonoid b) => GMonoid (a, b) 
GMonoid a => GMonoid (Const a b) 
(GMonoid a, GMonoid b, GMonoid c) => GMonoid (a, b, c) 
(GMonoid a, GMonoid b, GMonoid c, GMonoid d) => GMonoid (a, b, c, d) 
(GMonoid a, GMonoid b, GMonoid c, GMonoid d, GMonoid e) => GMonoid (a, b, c, d, e) 
(GMonoid a, GMonoid b, GMonoid c, GMonoid d, GMonoid e, GMonoid f) => GMonoid (a, b, c, d, e, f) 
(GMonoid a, GMonoid b, GMonoid c, GMonoid d, GMonoid e, GMonoid f, GMonoid g) => GMonoid (a, b, c, d, e, f, g) 
(GMonoid a, GMonoid b, GMonoid c, GMonoid d, GMonoid e, GMonoid f, GMonoid g, GMonoid h) => GMonoid (a, b, c, d, e, f, g, h) 

Default definitions

GMonoid

gmemptydefault :: (Generic a, GMonoid' (Rep a)) => a

gmappenddefault :: (Generic a, GMonoid' (Rep a)) => a -> a -> a

Internal auxiliary class for GMonoid

class GMonoid' f where

Methods

gmempty' :: f x

gmappend' :: f x -> f x -> f x

Instances

GMonoid' * U1 
GMonoid a => GMonoid' * (K1 i a) 
(GMonoid' * f, GMonoid' * h) => GMonoid' * (:*: f h) 
GMonoid' * f => GMonoid' * (M1 i c f) 

Monoid

These functions can be used in a Monoid instance. For example: 

  -- LANGUAGE DeriveGeneric

import Generics.Deriving.Base (Generic)
  import Generics.Deriving.Monoid

data T a = C a (Maybe a) deriving Generic

instance Monoid a => Monoid (T a) where
    mempty  = memptydefault
    mappend = mappenddefault

memptydefault :: (Generic a, Monoid' (Rep a)) => a

mappenddefault :: (Generic a, Monoid' (Rep a)) => a -> a -> a

Internal auxiliary class for Monoid

class Monoid' f where

Methods

mempty' :: f x

mappend' :: f x -> f x -> f x

Instances

Monoid' * U1 
Monoid a => Monoid' * (K1 i a) 
(Monoid' * f, Monoid' * h) => Monoid' * (:*: f h) 
Monoid' * f => Monoid' * (M1 i c f) 

The Monoid module

This is exported for convenient access to the various wrapper types.