61–70 of 187 posts
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.
As far as monad tutorials go, this one seems quite good. I like the categorization of monads between "containers" and "recipes". However, I personally think that monad tutorials tend to give people the wrong impression and leave them more confused than they were before, because they focus on the wrong thing. A monad is not a complex concept, at all. IMO a more useful way to present the topic would be with one separat…
Earlier quoted context omitted.
Lots of useful generic code. MapM is a version of `map` that works with any Monad, `sequence` works with any monad, and so on. These are used very frequently. But the bigger benefit is when syntax sugar like `do` notation comes in. Because it works for any Monad, people can write their own Monads and take advantage of the syntax sugar. That leads to an explosion of creativity unavailable to languages who "lock down"…
What can a Haskell monad do that a Python class cannot? 99% of all monads I've seen only facilitate local state manipulation.
foo ::
_ =>
Exception String e1 ->
State Int e2 ->
Eff es Bool
foo = ...
So, that's what you get in Haskell that Python doesn't give you.
While I can understand the desire to draw a metaphor, there are better approaches than saying, "A List Is a Monad". The statement as-is breaks pretty much immediately because, while there is a canonical list monad, there isn't a list monad, there are in fact several[1]. There are several more correct ways of phrasing the idea among: "List can be given a monad instance" "List forms a monad with pure and bind as define…
The way I think of it, monads are a solution to Callback Hell, where you've fallen in love with lambdas, but now you have a nightmarish mess of lambdas in lambdas and lambdas calling lambdas. The monadic functions allow you to create "for comprehensions" aka "do comprehensions" but really, they look like a classic for-each loop. They secretly call the monadic map/flatMap/filter functions. for x in list doThings(x) Th…
After reading your comment, I've made it my mission to understand it. Although I have no idea what you're talking about, you make it sound intriguing.
As far as monad tutorials go, this one seems quite good. I like the categorization of monads between "containers" and "recipes". However, I personally think that monad tutorials tend to give people the wrong impression and leave them more confused than they were before, because they focus on the wrong thing. A monad is not a complex concept, at all. IMO a more useful way to present the topic would be with one separat…
If all monad instances work differently what is the value of the Monad interface? What kind of usefull generic code can one write against the Monad interface. Related: https://buttondown.com/j2kun/archive/weak-and-strong-algebra...
https://hackage.haskell.org/package/base-4.21.0.0/docs/Contr...
https://hackage.haskell.org/package/base-4.21.0.0/docs/Data-...
As far as monad tutorials go, this one seems quite good. I like the categorization of monads between "containers" and "recipes". However, I personally think that monad tutorials tend to give people the wrong impression and leave them more confused than they were before, because they focus on the wrong thing. A monad is not a complex concept, at all. IMO a more useful way to present the topic would be with one separat…
If all monad instances work differently what is the value of the Monad interface? What kind of usefull generic code can one write against the Monad interface. Related: https://buttondown.com/j2kun/archive/weak-and-strong-algebra...
The way I think of it, monads are a solution to Callback Hell, where you've fallen in love with lambdas, but now you have a nightmarish mess of lambdas in lambdas and lambdas calling lambdas. The monadic functions allow you to create "for comprehensions" aka "do comprehensions" but really, they look like a classic for-each loop. They secretly call the monadic map/flatMap/filter functions. for x in list doThings(x) Th…
After reading your comment, I've made it my mission to understand it. Although I have no idea what you're talking about, you make it sound intriguing.
With those caveats in mind, here's a more intensive scala-based monad tutorial I made:
https://github.com/zaboople/techknow/blob/master/scala/monad...
But really, don't burn up too much of your short life trying to come to terms with this stuff. There's a reason most languages don't get around to supporting Monads...
Earlier quoted context omitted.
What can a Haskell monad do that a Python class cannot? 99% of all monads I've seen only facilitate local state manipulation.
This may be a dissenting opinion, but... Haskell tried to avoid mutable state. "Local state manipulation" was not really a thing you could do in Haskell, deliberately. Then someone figured out that you could (ab)use a monad to do that. And because that was the only way, whenever they needed to manipulate state, Haskell programmers reached for a monad. So it's not "what can a Haskell monad do that a Python class canno…
So, they're certainly not a means of getting around a limitation of the language. If it was just a limitation that limitation would have been lifted a long time ago! It's a means of preserving a desirable property of the language (referential transparency) whilst also preserving access to mutable state, exceptions, I/O, and all sorts of other things one expects in a normal language.
See my comment here for a little bit more about the benefits of referential transparency: https://news.ycombinator.com/item?id=44448127
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.
Could you elaborate on that? What does 'flatMappable' mean in this context?
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...