group-theory-0.2.2: The theory of groups
Copyright(c) 2020-2021 Reed Mullanix Emily Pillmore
LicenseBSD-style
MaintainerReed Mullanix <reedmullanix@gmail.com>, Emily Pillmore <emilypi@cohomolo.gy>
Stabilitystable
Portabilitynon-portable
Safe HaskellSafe
LanguageHaskell2010

Data.Group.Foldable

Description

This module provides definitions GroupFoldable, along with useful combinators.

Synopsis

Group foldable

class GroupFoldable t where Source #

The class of data structures that can be groupoidally folded.

GroupFoldable has difficult-to-define laws in terms of Haskell, but is well-understood categorically: GroupFoldables are functors (not necessarily Functors) in the slice category \( [\mathcal{Hask}, \mathcal{Hask}] / F \), where \( F \) is the free group functor. Hence, they are defined by the natural transformations \( [\mathcal{Hask},\mathcal{Hask}](-, F) \) - i.e. toFG, or toFreeGroup.

Minimal complete definition

goldMap | toFG

Methods

goldMap :: Group g => (a -> g) -> t a -> g Source #

Apply a Group fold to some container.

This function takes a container that can be represented as a FreeGroup, and simplifies the container as a word in the free group, producing a final output according to some mapping of elements into the target group.

The name is a pun on Group and fold.

Examples:

>>> let x = FreeGroup $ [Left (1 :: Sum Word8), Left 2, Right 2, Right 3]
>>> goldMap id x
Sum {getSum = 2}
>>> goldMap (\a -> if a < 2 then mempty else a) x
Sum {getSum = 3}

toFG :: t a -> FG a Source #

Translate a GroupFoldable container into a Church-encoded free group.

Analagous to toList for Foldable, if toList respected the associativity of ⊥.

Instances

Instances details
GroupFoldable Identity Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> Identity a -> g Source #

toFG :: Identity a -> FG a Source #

GroupFoldable Dual Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> Dual a -> g Source #

toFG :: Dual a -> FG a Source #

GroupFoldable Sum Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> Sum a -> g Source #

toFG :: Sum a -> FG a Source #

GroupFoldable Product Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> Product a -> g Source #

toFG :: Product a -> FG a Source #

GroupFoldable Abelianizer Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> Abelianizer a -> g Source #

toFG :: Abelianizer a -> FG a Source #

GroupFoldable FreeGroup Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> FreeGroup a -> g Source #

toFG :: FreeGroup a -> FG a Source #

GroupFoldable FG Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a -> g) -> FG a -> g Source #

toFG :: FG a -> FG a Source #

GroupFoldable (Const a :: Type -> Type) Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g => (a0 -> g) -> Const a a0 -> g Source #

toFG :: Const a a0 -> FG a0 Source #

(GroupFoldable f, GroupFoldable g) => GroupFoldable (f :+: g) Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g0 => (a -> g0) -> (f :+: g) a -> g0 Source #

toFG :: (f :+: g) a -> FG a Source #

(GroupFoldable f, GroupFoldable g) => GroupFoldable (f :*: g) Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g0 => (a -> g0) -> (f :*: g) a -> g0 Source #

toFG :: (f :*: g) a -> FG a Source #

(GroupFoldable f, GroupFoldable g) => GroupFoldable (f :.: g) Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g0 => (a -> g0) -> (f :.: g) a -> g0 Source #

toFG :: (f :.: g) a -> FG a Source #

(GroupFoldable f, GroupFoldable g) => GroupFoldable (Compose f g) Source # 
Instance details

Defined in Data.Group.Foldable

Methods

goldMap :: Group g0 => (a -> g0) -> Compose f g a -> g0 Source #

toFG :: Compose f g a -> FG a Source #

Group foldable combinators

gold :: (GroupFoldable t, Group g) => t g -> g Source #

Simplify a word in GroupFoldable container as a word in a FreeGroup.

The name is a pun on Group and fold.

Examples:

>>> let x = FreeGroup $ [Left (1 :: Sum Word8), Left 2, Right 2, Right 3]
>>> gold x
Sum {getSum = 2}

goldr :: GroupFoldable t => Group g => (a -> Permutation g) -> t a -> Permutation g Source #

A right group fold from a GroupFoldable container to its permutation group

Analogous to foldr for monoidal Foldables.

toFreeGroup :: (GroupFoldable t, Group g) => t g -> FreeGroup g Source #

Convert a GroupFoldable container into a FreeGroup