regular-0.2: Generic programming library for regular datatypes. Source code Contents Index

Generics.Regular.Functions.Fold Portability non-portable Stability experimental Maintainer generics@haskell.org

Contents Generic folding Generic unfolding Construction of algebras

Description

Summary: Generic folding and unfolding.

Synopsis

type family Alg f r :: * type Algebra a r = Alg (PF a) r class Fold f where alg :: Alg f r -> f r -> r fold :: (Regular a, Fold (PF a), Functor (PF a)) => Algebra a r -> a -> r type family CoAlg f s :: * type CoAlgebra a s = s -> CoAlg (PF a) s class Unfold f where coalg :: (s -> a) -> CoAlg f s -> f a unfold :: (Unfold (PF a), Regular a) => CoAlgebra a s -> s -> a (&) :: a -> b -> (a, b)

Generic folding

type family Alg f r :: * Source

type Algebra a r = Alg (PF a) r Source

class Fold f where Source

The class fold explains how to convert an algebra Alg into a function from functor to result. Methods alg :: Alg f r -> f r -> r Source Instances Fold U Fold I Fold (K a) Fold f => Fold (S s f) Fold f => Fold (C c f) Fold g => Fold (I :*: g) Fold g => Fold (K a :*: g) (Fold f, Fold g) => Fold (f :+: g)

fold :: (Regular a, Fold (PF a), Functor (PF a)) => Algebra a r -> a -> r Source

Fold with convenient algebras.

Generic unfolding

type family CoAlg f s :: * Source

type CoAlgebra a s = s -> CoAlg (PF a) s Source

class Unfold f where Source

The class unfold explains how to convert a coalgebra CoAlg and a seed into a representation. Methods coalg :: (s -> a) -> CoAlg f s -> f a Source Instances Unfold U Unfold I Unfold (K a) Unfold f => Unfold (S s f) Unfold f => Unfold (C c f) (Unfold f, Unfold g) => Unfold (f :*: g) (Unfold f, Unfold g) => Unfold (f :+: g)

unfold :: (Unfold (PF a), Regular a) => CoAlgebra a s -> s -> a Source

Construction of algebras

(&) :: a -> b -> (a, b) Source

For constructing algebras it is helpful to use this pairing combinator.

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