Ranges in Swift

Ranges.swift

// <a..b> <a..b| |a..b> |a..b|

operator prefix  | { }
operator postfix | { }
operator prefix  < { }
operator postfix > { }

enum Bound<T: ForwardIndex> {
    case Closed (@auto_closure () -> T)
    case Open   (@auto_closure () -> T)
}

@prefix func  | <T: ForwardIndex> (x: T) -> Bound<T> { return .Open   (x) }
@postfix func | <T: ForwardIndex> (x: T) -> Bound<T> { return .Open   (x) }
@prefix func  < <T: ForwardIndex> (x: T) -> Bound<T> { return .Closed (x) }
@postfix func > <T: ForwardIndex> (x: T) -> Bound<T> { return .Closed (x) }

@infix func .. <T: ForwardIndex> (f: Bound<T>, t: Bound<T>) -> Range<T> {
    switch (f, t) {
    case (.Closed (let x), .Closed (let y)): return x()...y()
    case (.Closed (let x), .Open   (let y)): return x()..<y()
    case (.Open   (let x), .Closed (let y)): return x().successor()...y()
    case (.Open   (let x), .Open   (let y)): return x().successor()..<y()
    }
}