Swift Programming Language (Apple) Predicate<T>

main.swift

let iseven = Predicate { (n:Int) -> Bool in n % 2 == 0 }

iseven[7]
iseven[6]

Predicate.swift

class Predicate<T> {
    let pred:(T) -> Bool
    init(pred:(T) -> Bool) {
        self.pred = pred
    }
    subscript(input:T) -> Bool {
        get {
            return pred(input)
        }
    }
}