# Functor

A *uniform transformation* `(a -> b)`

over *a parameterized type* `f`

, which is also called **mapping**.

A parameterized type is basically everything, from *Lists* and *Strings* to *functions* itselves.

## Haskell

*To be* a Functor is to implement the `fmap`

function which applies a function.

class Functor f where fmap :: (a -> b) -> f a -> f b

"Lifted" application, analogous to `($)`

.

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

An infix synonym of `fmap`

*substituting a constant* instead of function application (transformation)

(<$) :: a -> f b -> f a (<$) = fmap . const

Last modified
23 months ago
Last modified on Apr 5, 2018, 5:17:00 AM

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