Function combinators

FunctionCombinators.swift

/* -------------- Higher order function combinators ---------------- */
// Composition operators

infix operator >>>
func >>> <A,B,C> (aToB: @escaping (A) -> B, bToC: @escaping (B) -> C) -> (A) -> C {
    return { a in aToB(a) |> bToC }
}

infix operator <<<
func <<< <A,B,C> (bToC: @escaping (B) -> C, aToB: @escaping (A) -> B) -> (A) -> C {
    return { a in bToC <| aToB(a) }
}

// Pipe operators
infix operator |>
func |> <B,C> (value: B, bToC: (B) -> C) -> C {
   return bToC(value)
}

infix operator <|
func <| <B,C> (bToC: (B) -> C, value: B) -> C {
   return bToC(value)
}
// Arrow like operators (&&&)
infix operator &&&
func &&& <B,C,D> (bToC: @escaping (B) -> C, bToD: @escaping (B) -> D) -> (B) -> (C, D) {
    return { b in (bToC(b), bToD(b)) }
}


// MARK: - TEST

let incrementar = {x in x + 1}
let duplicar = {x in x * 2}
let even = {x in x % 2 == 0 }
let greaterThan3 = { x in x > 3 }

let test1 = incrementar(3) |> duplicar
print(test1)

let test2 = incrementar >>> duplicar
print(test2(5))

let test3 = (even &&& greaterThan3) >>> { (f ,s) in f && s }
print(test3(6))