[ddragon]

Each language will have different design priorities. For example auto-currying is great but it wouldn't make sense in a multiple dispatch language since you have to evaluate every argument to dispatch (which makes n-arity functions necessarily first class, not a composition of 1-arity functions). Another example is that Julia's type system exists to make it more dynamic (while maintaining high performance), while ML languages focus on static properties.

But previous designs are great for inspiration (like you say, Julia has a lot from them, like sum and product types, subtyping, parametric polymorphism) in the same way it also borrows from Lisp (CLOS). You can probably find in the literature/issues/discussion if you're curious how the language ended up this way, for example:

https://arxiv.org/abs/1808.03370

[greggyb]

> auto-currying is great but it wouldn't make sense in a multiple dispatch language since you have to evaluate every argument to dispatch (which makes n-arity functions necessarily first class, not a composition of 1-arity functions).

I have a question on this. I'll note up front that this is not an area of expertise for me.

It seems like knowledge of the types is/could be embedded in the process of currying. Multiple dispatch of a 2-ary function depends on the type of arg1 and arg2. If I call this with just the first arg, then the curried function "has knowledge" of the type of arg1. So now I have a 1-ary function that can do single dispatch on the type of its argument.

This seems possible to me to inductively extend to n-ary functions, since the process of consuming one argument by currying embeds knowledge of the type of that arg in the newly created function of n-1 arity.

Am I way off base here?

[ddragon]

I'm very far from an expert as well, but as I see you could have automatic currying in the same way I can write in Julia x -> f(x, 10) (manual currying using anonymous function) but automatically for every function. But the language would have to disallow using them for dispatch purposes:

f :: (Int -> Double) -> Int -> Double

That would have to dispatch to

f(::Function(::Int, ::Double), ::Int)::Double

Now the dispatch will have to be recursive (it will have to apply to each argument and arguments arguments to evaluate which is more specialized), making finding the most specialized version of a function even more chaotic. I'm trying not to think what dispatching on return types means for the compiler though (and that's not necessary for the auto currying).

And because of the currying, if you apply the first argument you'd have a (g :: Int -> Double) which has the memory of receiving (Int -> Double). But now trying to dispatch on another function with that partial will it dispatch as if it were a normal Int -> Double or will the "knowledge" of receiving a previous argument change which method it will pick?

To be honest I have no idea, it's probably possible but it feels like it would be something very different from Julia.

[higherkinded]

>which makes n-arity functions necessarily first-class

Excuse me but tuples. You still have to observe them to evaluate them but that's all you need to simulate n-arity in the way you want.

>more dynamic

Well, Hindley—Milner is how you do type-safe stuff with inference that annotates for you. For any generic purposes you just put a typevar with constraints, so I don't see a problem here and can't really get what you gain. MLs are more about proper composition.