You're using jquery as a functor not a monad.
> No, you have a completely incorrect understanding of Monads.
To re-use your slightly ad-hominem argument structure: "No, you have a completely incorrect understanding of Monads!" Of course the word "completely" here is just an unnecessarily flamebaity word choice in describing either of us. Clearly, we both have some understanding of monads. Let's look at the facts instead:
A functor applies an operation to a wrapped value. But monads apply functions that also return a wrapped value. It should be easy to see why people think the jQuery chain pattern is indeed monadic.
For what it's worth, I'm far from alone in asserting that jQuery is indeed a monad.
Since Haskell people claim to be the only enablers of "true monads", they would of course nitpick about patterns implemented in other languages. But religion aside, the OP asked for the possible uses of monads, and there they are. That the example also shows functors is just an added benefit, though not at all relevant to the discussion.
And a lot of people think that the reason astronauts float on the ISS is because there's no gravity there.
> Since Haskell people claim to be the only enablers of "true monads", they would of course nitpick about patterns implemented in other languages.
Yes, because monad is an actual term and calling something a monad just because it sort of looks like it if you squint doesn't make it one. You can't write return in the 'jQuery monad', because there's no way to wrap arbitrary data types, only things like DOM elements. Something like a promise is closer to a monad, because you can turn any value into a promise, but IIRC there are still issues around it that I don't remember offhand.
He describes monads as "a loophole" in the idea of function purity. This isn't true; monads aren't a way to 'cheat' any more than passing an accumulator through like
factorial acc 1 = acc
factorial acc n = factorial (acc * n) (n - 1)
He also calls values 'monads', which isn't accurate terminology at all; they're usually called monadic actions.
Yes, but they also must follow the monad laws.
>It should be easy to see why people think the jQuery chain pattern is indeed monadic.
It is not easy for me to see. In any of your examples are you returning the same encapsulated structure in your lambda you pass in? It doesn't look like it.
>For what it's worth, I'm far from alone in asserting that jQuery is indeed a monad.
Yes, a lot of people have a misunderstanding of monads.
>Since Haskell people claim to be the only enablers of "true monads",
I'm not a Haskell person. I write monadic code in both Scala and C# to great effect.
In fact if you used jQuery, you already know what a Monad is, probably without realizing it. Consider the following code:
You can follow along what this code does by following the dots. First, all elements matching the ".myelements" class are returned, these are then filtered, and the result of that gets a css modification.Every time you wrote a method that returns an object, you already did monads in principle. They can be used to chain things together. While Haskell provides semantics that explicitly deal with the mechanics of monads, pretty much every dynamic language has them.
Here's what it looks like in PHP, for example:
You can use monads to make your code more concise, to simply chain function calls, or to iterate over a list, but they're also often used when sifting through databases since filtering and applying attributes to items. For example, an SQL-like database query might be expressed like this: Of course, that's an API which is a bit dishonest since it acts as if the code really goes through all those items (which would be a performance disaster with huge databases), so when you see something like this it's often just a shortcut to assemble a query. And this goes for monads in general, they're really more of an API style. A monad itself is an abstract concept, a paradigm.> Also, it's suspicious that pg has never once mentioned monads
For a theory why pg specifically hasn't written anything about monads yet, here's an article that I believe was on HN in the past about the difficulties of comfortably using monads in Lisp: http://marijnhaverbeke.nl/monad.html - but I guess the short explanation would probably be that Lispers tend to deal with monad-worthy problems in other ways.