Data.Generics.Traversable.Generic

For a datatype where every subterm is interesting, it is possible to leverage Generic to automatically produce the GTraversable instance.

This module defines a default GTraversable instance for most Generic types, though you can override it with a custom instance if you so wish. The gtraverse implementation for this instance traverses every subterm, and traverses left-to-right on products :*:.

Example usage:

{-# LANGUAGE FlexibleInstances, DeriveGeneric #-}
import Data.Maybe (isJust)

data MyConfig = MyConfig
  { firstKey  :: Maybe Int
  , secondKey :: Maybe String
  , thirdKey  :: Maybe Bool
  }
  deriving (Generic)

class SettableConfigKey a where
  isSet :: a -> Bool

instance SettableConfigKey (Maybe a) where
  isSet = isJust

isAnyConfigKeySet :: MyConfig -> Bool
isAnyConfigKeySet = gfoldr @SettableConfigKey ((||) . isSet)

For Generic types that have Rec1 in their representation, this module will not work for GHC versions below 8.6.1, as the instance makes use of QuantifiedConstraints. Instead, the instance for Rec1 will cause a type error.

Documentation

class GTraversable' c (f :: * -> *) where

Special version of GTraversable for the representation types from Generic.

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. f p -> g (f p)

Instances

GTraversable' c Par1

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. Par1 p -> g (Par1 p)

GTraversable' c (V1 :: Type -> Type)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. V1 p -> g (V1 p)

GTraversable' c (U1 :: Type -> Type)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. U1 p -> g (U1 p)

(forall p. GTraversable c (f p)) => GTraversable' c (Rec1 f)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. Rec1 f p -> g (Rec1 f p)

(GTraversable' c f, GTraversable' c g) => GTraversable' c (f :*: g)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g0 => (forall d. c d => d -> g0 d) -> forall p. (f :*: g) p -> g0 ((f :*: g) p)

(GTraversable' c f, GTraversable' c g) => GTraversable' c (f :+: g)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g0 => (forall d. c d => d -> g0 d) -> forall p. (f :+: g) p -> g0 ((f :+: g) p)

c con => GTraversable' c (K1 i con :: Type -> Type)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. K1 i con p -> g (K1 i con p)

(Traversable f, GTraversable' c g) => GTraversable' c (f :.: g)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g0 => (forall d. c d => d -> g0 d) -> forall p. (f :.: g) p -> g0 ((f :.: g) p)

GTraversable' c f => GTraversable' c (M1 i meta f)

Defined in Data.Generics.Traversable.Generic

Methods

gtraverse' :: Applicative g => (forall d. c d => d -> g d) -> forall p. M1 i meta f p -> g (M1 i meta f p)

Orphan instances

(Generic a, GTraversable' c (Rep a)) => GTraversable c a

Methods

gtraverse :: Applicative f => (forall d. c d => d -> f d) -> a -> f a