Partition and Choose

gistfile1.swift

operator infix |> {associativity left precedence 140}
func |> <T,U> (left: @auto_closure () -> T,right: T -> U) -> U {
    return right(left())
}

func partition<T>(f : T -> Bool)(a : Array<T>) -> (left: Array<T>, right: Array<T>) {
    var (leftpartition,rightpartition) = (Array<T>(),Array<T>())
    for (index, value) in enumerate(a) {
        if f(value) {
            leftpartition.append(value)
        }
        else {
            rightpartition.append(value)
        }
    }
    return (leftpartition,rightpartition)
}

func choose<S,T>(f : S -> T?)(a : Array<S>) -> Array<T> {
    var result = Array<T>()
    for (index, value) in enumerate(a) {
        if let r = f(value) {
            result.append(r)
        }
    }
    return result
}


func greaterThan(n : Int)(v : Int) -> Bool {return n >= v}
let greaterThanThree = greaterThan(3)
let greaterThanFive = greaterThan(5)

let (left,right) = [1,2,3,4,5,6] |> partition (greaterThanThree)
//left will be [1,2,3]
// right will be [4,5,6]
left
right
let (left1,right1) = [1,2,3,4,5,6] |> partition (greaterThanFive)


left1
right1


let nils = [1,2,3,4,5] |> choose {(n : Int) -> Int? in return n > 3 ? n : nil}
nils