product.groovy

//Cartesian product of input (for Integers)
//similar to itertools.product in Python

def l = [ [1,2] , [3,4] , [5, 6]]

def product(l){
    def p = { l1, l2 ->
        l1.inject([]) { acc, i ->
            acc + l2.inject([]) { acc1, j ->
                if ( i instanceof List) { acc1 << i + j} 
                else { acc1 << [i, j]}}}}

        l.inject() { acc, it -> p(acc, it) }
}

println  product(l)

//[[1, 3, 5], [1, 3, 6], [1, 4, 5], [1, 4, 6], [2, 3, 5], [2, 3, 6], [2, 4, 5], [2, 4, 6]]