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A list is a monad

(alexyorke.github.io)
153 points polygot | 2 comments | 29 Jun 25 17:53 UTC | HN request time: 0.436s | source
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drumnerd ◴[02 Jul 25 19:12 UTC] No.44447662[source]▶
A monad is not a container! It’s a way of composing functions if they have an effect. You tell how to inject a value in that effect (unit) and how to compose two functions that have that effect and that’s it: programmable semicolons.
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1. polygot ◴[02 Jul 25 20:30 UTC] No.44448492[source]▶
Thanks for the feedback, I totally agree that monads are not containers. From an OOP perspective, they have some properties that make them, in some sense, sorta like containers, e.g., they contain a value like the Maybe monad. I still agree that they are not simply containers. I can clarify this in a revision to part 1 soon.
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2. lmm ◴[03 Jul 25 01:59 UTC] No.44450903[source]▶
> From an OOP perspective, they have some properties that make them, in some sense, sorta like containers, e.g., they contain a value like the Maybe monad.

Not always! I find this is a big source of confusion; not all monads contain values, sometimes beginners think they can or should "get the value out" of a monad and that tends to lead to writing the wrong kind of code.