# fmap with a function

What is this code doing?

## Answer¶

`fmap`

is the method of the Functor typeclass.

To understand what `fmap`

does whenever it is called, it is necessary to know which *instance* of `fmap`

is being used. You can find this out by mousing over `fmap`

(first place the line `func = fmap not (\x -> x > 3)`

in a Haskell file in your project), to see:

The line `$dFunctor :: Functor ((->) Integer)`

means that the instance of `Functor`

being used is `((->) Integer)`

.

The instance of `Functor`

for `((->) Integer)`

is:

- Or in pointfree style: fmap = (.)

and this is what is being used in the examples above.

Last update:
January 17, 2023

Created: January 13, 2023

Created: January 13, 2023