Pointfree Ep1 Functions

Guowei Lv

1 minute read

I’m starting a new series, mostly just me taking notes while I go through the PointFree videos.

The pipe operator

The |> operator is defined as:

precedencegroup ForwardApplication {
  associativity: left
}

infix operator |>: ForwardApplication

func |> <A, B>(x: A, f: (A) -> B) -> B {
  return f(x)
}

It can be used as::

func incr(_ x: Int) -> Int {
  return x + 1
}

func square(_ x: Int) -> Int {
  return x * x
}

2 |> incr |> square

Function composition operator

This operator is defined as: 

precedencegroup ForwardComposition {
  higherThan: ForwardApplication
  associativity: left
}
infix operator >>>: ForwardComposition

func >>> <A, B, C>(_ f: @escaping (A) -> B, _ g: @escaping (B) -> C) -> ((A) -> C) {
  return { a in g(f(a)) }
}

Now we can compose two functions(given that the types match) into a new one by: 

2 |> incr >>> square

[1, 2, 3].map(square >>> incr)

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