CODEWITHSUNDEEP
haskell
McBear Holden
McBear Holden

Reputation: 5901

What is the point of using Monad in a program?

Say i'm creating an image processing library with Haskell. I've defined a few of my own data types.

When should i declare some of my data types to be Monad(or functor or applicative functor etc) ? And what is the benefit of doing so?

I understand that if some data types can be "mapped over" then i can declare it to be an instance of functor. But if i do so what is the benefit ?

This might be a really silly question but i'm still struggling my way into the functional programming realm.

Upvotes: 4

Views: 198

Answers (1)

Ben
Ben

Reputation: 71400

The point is basically the same as the point of using any useful abstract interface in OO programming; all the code that already exists that does useful things in terms of that interface now works on your new type.

There's nothing that says you have to make anything an instance of Monad that could be, and it won't enable you to really do anything you couldn't do anyway. But if you don't, it's practically guaranteed that some of the code you write will in fact be re-implementing things that are equivalent to existing code that works on any monad; probably you will do so without realising it.

If you're not very familiar/confident with the Monad interface, recognising this redundancy and removing it will probably be more effort than just writing the repeated code. But if you do gain that familiarity, then spotting things that could be Monads becomes fairly natural, as does spotting code you were about to write that could be replaced by existing Monad code. Again, this is pretty similar to generically useful abstract interfaces in OO languages; mainstream OO languages just tend to lack the type system features necessary to express the concept of general monads, so it's not one that many OO programmers have already gotten familiar with. As with anything in programming, the best way to gain that familiarity is to just work with it for a while, and stumble through that period where everything takes longer than doing it some other way you're already comfortable with.

Monad is nothing but a very generally useful interface. Monads are particularly useful in Haskell because they have been accepted by the community as standard, so lots of existing library code works with them. But there's really nothing more magical to them than that.

Upvotes: 6

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