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Comment by a-saleh | Hacker News Reader

Funny, I already kinda use partial application in Javascript, just by using curried functions a lot. I.e.

const add = x => y => x + y

This is definitely non-idiomatic, but the definition syntax itself doesn't look that bad, if you can stomach writing add(1)(2) to use it.

I do agree that using _ would probably be a better solution :-)

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Right, this is currying not partial application. And it comes with the drawback that you always have to call the function multiple times. You can't provide all the parameters in one list, which rules out things like spread arguments. That's not the case with `param.macro`, depending on how you apply of course.

Am I missing something? Why not just

const add = (a,b)=>a+b?

You can not use partial application with that. for example const add = x=>y=>x+y

can be partialy applied like the following const add3 = add(3) // this is also a function

> You can not use partial application with that.

You can:

    const add3 = add.bind(null, 3)

I still like currying better, but I just might be weird like that :-)

I only asserted that you could partially apply regular functions. But I don't think currying looks or feels nice in Javascript.

Proper curried languages are definitely better suited for partial application though.

You could use default parameters in this case.

const add = (a, b=0) => {return a+b}

Well usually it would be for something that is useful, like

const greaterThan = x => y => y > x

and then I can do thins like

numbers.filter(greaterThan(10))

because greatherThan(10) is a function (and I hope I did put the correct comparison operator :)

It also works better on languages using free functions than those using method calls e.g. in Haskell you have

    filter :: (a -> Bool) -> [a] -> [a]

so you partially apply to a predicate to get a specific filter condition which you can apply to various contexts e.g.

    over10 = filter (>= 10)

That's why functional languages tend to put the callback first in HoFs, it's usually the more common partial application case.

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