[gr4vityWall]

I think the most intuitive description for a monad I've ever seen is 'flatMappable'.

Context: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

Usually articles that describe them in a very Math-y way go above my head. But the definition above was immediately clear (I saw it on HN).

I think this article is a bit more approachable than others I've read, but it still gets very confusing near the end.

[hirvi74]

Reminds me on an analogy for a monad I once heard. Not sure if it is correct because I lack the mathematical understanding to verify.

Anyway, a nested To-Do list is (allegedly) a common form of a monad. Say I am trying to clean my whole house. Well, I could have an item for a task like cleaning the kitchen that has each task I need to do in the kitchen in order for the kitchen to be cleaned. I can do the same for the living room, garage, etc..

However, that is mainly for organization purposes. While I may write the tasks in a nested manner, I could very well write each item as just a long flat list of To-Do tasks, and in reality, all the tasks are effectively completed as if they were one large flat list.

Is that kind of what you mean by 'flatMappable'? Nested To-Do lists being flattened and mapped to one large list? As in, a To-Do list of To-Do lists is just a single, larger To-Do list?

[skybrian]

Not exactly. The flatMap() operation itself isn’t going to flatten an arbitrarily nested todo list. It just concatenates the lists that are returned after applying the callback to each item.

The monad part is about what happens if you call flatMap() repeatedly. That is, each call to flatMap() is one action, and these actions can be nested without affecting the result.

[gr4vityWall]

Yes, your understanding is correct. It's literally calling map() on an array, followed by a flat().

Sorry, I should have added more context to my post. I edited my post and added a link to the MDN definition of the flatMap function.

[aadhavans]

Could you elaborate on that? What does 'flatMappable' mean in this context?

[IshKebab]

This is a good explanation:

https://users.scala-lang.org/t/what-is-a-monad-in-scala/4169

It's like... what would you call all types that have a .write() method? Writable right? What would you call all types that have a .dispose() method? Disposable. What would you call all types that have a .flatMap() method? Monad obviously.

[skybrian]

That’s because flatMap() is a good name for a particular list operation, but it’s not generic enough to be a good name for the corresponding monad operation.

I’m not sure there is a good name for the monad operation. Sometimes it’s called ‘bind’ but what does it bind?

I suppose you could call it ‘then’ like when working with Promises.

[still_grokking]

Scala's new effect library Kyo just uses `map`. See:

https://getkyo.io/#/?id=the-quotpendingquot-type-lt

All pure values are automatically lifted into the Kyo monad, so `map` is effectively `flatMap`.

From the linked docs:

> This unique property removes the need to juggle between map and flatMap. All values are automatically promoted to a Kyo computation with zero pending effects, enabling you to focus on your application logic rather than the intricacies of effect handling.

In the end it makes a lot of sense I think. What you do is manipulating values inside some wrapper. Whether this wrapper is a monad or not should not matter. Just do something with the value(s) inside, and that's mapping.

[gr4vityWall]

something that you can call flatMap() on.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...