Functor

container

So, What are Functors? (JavaScript)

“Functors” are the containers or type that can be used with “map” function.

Graphic

graph LR; A[Functor]

Example:

Container.prototype.map = (f) => {
  return Container.of(f(this.$value));
};

Container.of(2).map(two => two + 2);

[1, 2, 3].map((num) => num + 2);

Just what is a Functor, really? (Haskell)

Functor is “typeclass” (A lot of people coming from OOP get confused by typeclasses because they think they are like classes in object oriented languages).

A Functor is any data type that defines how “fmap” applies to it. Here’s how “fmap” works: 

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

> fmap (+3) (Just 2)
-- Just 5

fmap

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