Swift: For a function that takes two arguments, return equivalent function with argument order reversed (like Haskell "flip")

flip.swift

// For a function that takes two arguments, return equivalent
// function with argument order reversed.
//
// (Like "flip" in Haskell prelude)
func flip<A, B, T>(f: (A, B) -> T) -> (B, A) -> T {
    return { (b: B, a: A) -> T in return f(a, b) }
}


// Examples

func subtract(a: Int, b: Int) -> Int {
    return a - b
}
let flippedSubtract = flip(subtract)

let result1 = subtract(10, 3)                     // 7
let result2 = flippedSubtract(10, 3)              // -7


func concat(s1: String, s2: String) -> String {
    return s1 + s2
}
let reverseConcat = flip(concat)

let result3 = concat("Hello, ", "world!")         // "Hello, world!"
let result4 = reverseConcat("Hello, ", "world!")  // "world!Hello, "