Agda.Utils.Functor

Utilities for functors.

Documentation

($>) :: Functor f => f a -> b -> f b infixr 4

(<.>) :: Functor m => (b -> c) -> (a -> m b) -> a -> m c infixr 9

Composition: pure function after functorial (monadic) function.

for :: Functor m => m a -> (a -> b) -> m b

The true pure for loop. for is a misnomer, it should be forA.

(<&>) :: Functor m => m a -> (a -> b) -> m b infix 4

Infix version of for.

class Functor t => Decoration t where

A decoration is a functor that is traversable into any functor.

The Functor superclass is given because of the limitations of the Haskell class system. traverseF actually implies functoriality.

Minimal complete definition: traverseF or distributeF.

Minimal complete definition

Nothing

Methods

traverseF :: Functor m => (a -> m b) -> t a -> m (t b)

traverseF is the defining property.

distributeF :: Functor m => t (m a) -> m (t a)

Decorations commute into any functor.

Instances

Decoration Identity

The identity functor is a decoration.

Decoration Ranged

Decoration WithHiding

Decoration Type'

Decoration Abs

Decoration Masked

Decoration ((,) a)

A typical decoration is pairing with some stuff.

Decoration (Named name)

Decoration (Dom c)

Decoration (Arg c)

(Decoration d, Decoration t) => Decoration (Compose d t)

Decorations compose. (Thus, they form a category.)

dmap :: Decoration t => (a -> b) -> t a -> t b

Any decoration is traversable with traverse = traverseF. Just like any Traversable is a functor, so is any decoration, given by just traverseF, a functor.

dget :: Decoration t => t a -> a

Any decoration is a lens. set is a special case of dmap.

The constant functor.

Maybe. Can only be traversed into pointed functors.

Other disjoint sum types, like lists etc.

(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4

An infix synonym for fmap.

Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing
Nothing
>>> show <$> Just 3
Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17
Left 17
>>> show <$> Right 17
Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3]
[2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)
(2,True)