Copyright	(C) 2012-2014 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell98

Control.Lens.Internal.Fold

Contents

Monoids for folding

Description

Synopsis

Monoids for folding

newtype Folding f a Source

A Monoid for a Contravariant Applicative.

Constructors

Folding
Fields getFolding :: f a

Instances

(Contravariant f, Applicative f) => Monoid (Folding f a)
(Contravariant f, Apply f) => Semigroup (Folding f a)

newtype Traversed a f Source

Used internally by traverseOf_ and the like.

The argument a of the result should not be used!

Constructors

Traversed
Fields getTraversed :: f a

Instances

Applicative f => Monoid (Traversed a f)
Apply f => Semigroup (Traversed a f)

newtype Sequenced a m Source

Used internally by mapM_ and the like.

The argument a of the result should not be used!

Constructors

Sequenced
Fields getSequenced :: m a

Instances

Monad m => Monoid (Sequenced a m)
Apply m => Semigroup (Sequenced a m)

data Max a Source

Used for maximumOf.

Constructors

NoMax
Max a

Instances

Ord a => Monoid (Max a)
Ord a => Semigroup (Max a)

getMax :: Max a -> Maybe a Source

Obtain the maximum.

data Min a Source

Used for minimumOf.

Constructors

NoMin
Min a

Instances

Ord a => Monoid (Min a)
Ord a => Semigroup (Min a)

getMin :: Min a -> Maybe a Source

Obtain the minimum.

data Leftmost a Source

Used for preview.

Constructors

LPure
LLeaf a
LStep (Leftmost a)

Instances

Monoid (Leftmost a)
Semigroup (Leftmost a)

getLeftmost :: Leftmost a -> Maybe a Source

Extract the Leftmost element. This will fairly eagerly determine that it can return Just the moment it sees any element at all.

data Rightmost a Source

Used for lastOf.

Constructors

RPure
RLeaf a
RStep (Rightmost a)

Instances

Monoid (Rightmost a)
Semigroup (Rightmost a)

getRightmost :: Rightmost a -> Maybe a Source

Extract the Rightmost element. This will fairly eagerly determine that it can return Just the moment it sees any element at all.

data ReifiedMonoid a Source

Constructors

ReifiedMonoid
Fields reifiedMappend :: a -> a -> a reifiedMempty :: a

newtype M a s Source

Constructors

M a

Instances

Reifies * s (ReifiedMonoid a) => Monoid (M a s)

reifyFold :: (a -> a -> a) -> a -> (forall s. Reifies s (ReifiedMonoid a) => t -> M a s) -> t -> a Source