===== Functor . Haskell =====
==== Haskell class ====
<code/Haskell> 
-- definition
class Functor f where
    fmap :: (a -> b) -> f a -> f b
    
-- methods
    (<$) :: a -> f b -> f a
    (<$) = fmap . const
</code>

| fmap id $\ \leftrightsquigarrow\ $ id |
| fmap f . fmap g $\ \leftrightsquigarrow\ $ fmap (f . g) |

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=== Discussion ===
In Haskell, the first law implies the second.

=== Notes ===
{{5815_89f1_500.png}}

=== Reference ===

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=== Related ===
[[Haskell]], [[Functor]], [[Functor category]]