Go: Generate all permutations of a slice or string

// Perm calls f with each permutation of a.
func Perm(a []rune, f func([]rune)) {
        perm(a, f, 0)
}

// Permute the values at index i to len(a)-1.
func perm(a []rune, f func([]rune), i int) {
        if i > len(a) {
                f(a)
                return
        }
        perm(a, f, i+1)
        for j := i + 1; j < len(a); j++ {
                a[i], a[j] = a[j], a[i]
                perm(a, f, i+1)
                a[i], a[j] = a[j], a[i]
        }
}

Example usage:

Perm([]rune("abc"), func(a []rune) {
        fmt.Println(string(a))
})

Output:

abc
acb
bac
bca
cba
cab