CODEWITHSUNDEEP
scala
softshipper
softshipper

Reputation: 34061

How currying works

I have following function with parameter lists:

def foo(a:Int, b:Int)(x:Int)(y:Int) = a * b + x - y

when I put the command on the relp

foo _

it shows me 

res5: (Int, Int) => Int => (Int => Int) = <function2>

The first part expects two int parameters and then I do not know anymore how to read continue.
I can use the function like

foo(5,5)(10)(10)

but I do not know how to read it!

Upvotes: 1

Views: 79

Answers (2)

Haito
Haito

Reputation: 2069

It's easy. (Int, Int) => Int => (Int => Int) means that 2 first steps returns a function that will take some arguments. For example:

(Int, Int) => Function that return
  (Int) => Function that return
    (Int) => Int

Why is it useful? Because when you have a function that take a function as parameter in of it's arguments list you can omit parentheses and use curly braces.

def someFunStuff(fun: Int)(stuff: Int => Int) = {
  fun*stuff(fun)
}

someFunStuff(2) { x =>
  //Do some fun stuff
  x * 2 / x
}

If you want to know a little bit more, please read Chapter 9.4 programming in Scala second edition.

Upvotes: 1

helios35
helios35

Reputation: 1637

In general, A => B is the type of an anonymous function that, when given an argument of type A, returns a value of type B. Now, the type (Int, Int) => Int => (Int => Int) might look less confusing when you add some parenthesis:

(Int, Int) => (Int => (Int => Int))

As a start, just break it down to

(Int, Int) => (… => …)

i.e. a function that, given two Int, returns another function. The function that is returned has type

(Int => (Int => Int))

i.e. a function that, given an Int, returns another function that, given an Int, returns an Int.

Upvotes: 2

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