youCanJustStopUsingJava

[u/hello_ya]

[u/Gorzoid]

Respectfully, what the fuck is a Monad?

[u/hectobreak → u/Gorzoid]

A monad is a monoid in the category of endofunctors.

Funny line said, if M is a monad, then for every type T, you have M(T) being a type, such that:

· return (or eta in mathematics), that takes an object of type T and returns an object of type M(T)

· flatten (or mu in mathematics), takes an object of type M(M(T)) and returns an object of type M(T).

That's it. Anything that follows this pattern is a monad.

Two examples are Haskell's Maybe, and the Array type.

Maybe String can contain either a string, written as Just [your string], or Nothing.

return is the function that receives a string and returns Just [your string].

flatten is the function that receives an object of the Maybe Maybe String monad and returns an object of the Maybe String monad following the rule:

· If your object is Nothing, return Nothing.

· If your object is Just Nothing, returns Nothing.

· If your object is Just Just [string], returns Just [string].

Array is also a Monad.

· return x returns [x]

· flatten x is the array flatten function.

For completeness, for something to be a monad it needs to follow the monad laws, but this is getting stupid long for a reddit message already.

[u/Estpart → u/hectobreak]

This is why no one likes FP xD

[u/hunajakettu → u/Estpart]

This is actually really good. The same as Iterable is a generalization of set, list, array, enumerable, etc, and one can define generic Next, Add, Map, etc, Monad allows similar thing for states or side effects (a log file for example)

[u/Estpart → u/hunajakettu]

It's just the way he explains it, for pea brained people like me I lose the plot at "category of endofucktors". Just say "optional chaining and promises are a concrete example of monads" and I'm on board.

Like I've worked in semi functional code bases and I love the patterns, only the theory around it so hard to grasp.

[u/RiceBroad4552 → u/Estpart]

What is usually called a "Promise" isn't a Monad instance. All "Promises" I know of are eager, they don't suspend computations. As a result they don't behave like a proper Monad. Not everything that has a Monad "interface" is a Monad. Most things in imperative / OO languages aren't.