monads.md

Monads

• Value, object.
• Data constructor, a box or a ghost box.
• Type constructor, a set of boxes.
• Type classes, classes of people who have a certain set of skills.

Clarification of ghost boxes:
They look like boxes, but actually you can directly touch the object inside them.
That is, the box is an illusion.

Maybe

Example set of boxes MAYBE:

• box Just
• box Nothing

Functor

Each class of people is trained to handle a box in a certain way.
Let's take a look at the people class FUNCTORS, skill set:

• skill fmap, description: execute an action on a box

For example, when a functor performs an fmap on a Just box,
he first opens the box, then executes the action on the item in the box,
then takes a new box of the same type and puts the item in the new box.

And when he performs an fmap on a Nothing box,
he just takes a new Nothing box, nothing more.

Monad

Let's look at another class of people, called MONADS,
these people have been mentored by the functors,
so they possess the same basic skillset:

• skill >>=, description: take a box and a box-producing machine,
  and do something with those things

When a monad receives a Just box, he knows that he first has to open the box,
get the item out of it and then put it in the machine.

Like the functor, when a monad receives a Nothing box,
he just takes a new Nothing box.