array_for_each(fn, a1, @rest...)
The function fn is applied to each element of the arrays a1, .... Fn must accept
as many arguments as there are arrays. The arrays must be of the same length.
Return void.
array_for_each(^(x, y) showln(x * y), #[1, 2, 3], #[4, 5, 6])
//-> 4
10
18