Discussion on: Ask me dumb questions about functional programming

[JavaScript Joel]

This is a great question!

First let's define arity as the number of arguments a function takes. This function is 2 arity.

const add = (x, y) => x + y

Currying is taking a 2+ arity function and splitting it into many 1 arity functions.

So if we were to curry add, it would look like this:

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

Now I would call the add function like this:

add (3) (4) //=> 7

Partial application is used with curried functions to partially apply arguments.

const add3 = add (3)
add3 (4) //=> 7

But partial application is not specific to curried functions either. For example, you could partially apply any non-curried function using bind.

const add = (x, y) => x + y
const add3 = add.bind(null, 3)

add3 (4) //=> 7

I hope that has been helpful!

Cheers!