Hashbang Swift

An easy way to run a swift code from the Terminal is by setting the hashbang (#!).

#!/usr/bin/xcrun swift -i

func hanoi<T>(numberOfDisks n :Int, fromRod f: T, toRod t: T, usingRod u: T, closure: (T, T) -> ()) {
    if n > 0 {
        hanoi(numberOfDisks: n - 1, fromRod: f, toRod: u, usingRod: t, closure)
        closure(f, t)
        hanoi(numberOfDisks: n - 1, fromRod: u, toRod: t, usingRod: f, closure)
    }
}

hanoi(numberOfDisks: 4, fromRod: "A", toRod: "B", usingRod: "C") {
    println("Move from \($0) to \($1)")
}

Once the hashbang is set, the file can have its mode bits changed to make it executable.

$ chmod +x hanoi.swift

And, finally, Swift running from the terminal:

$ ./hanoi.swift
Move from A to C
Move from A to B
Move from C to B
Move from A to C
Move from B to A
Move from B to C
Move from A to C
Move from A to B
Move from C to B
Move from C to A
Move from B to A
Move from C to B
Move from A to C
Move from A to B
Move from C to B

But note that the swift command is installed by Xcode 6, and it's not visible while Xcode 5 is the default Xcode set for development. To make it visible, it's necessary to switch to Xcode 6 by running the command xcrun

$ xcrun -s /Application/Xcode6-Beta2.app