say "Modifying while iterating:"
xs := [1,2,3,4]
for x in xs
    say "$x"
    xs.insert(10*x)

say "$xs"
fail unless "$xs" == "[1, 2, 3, 4, 10, 20, 30, 40]"

say "Modifying while iterating:"
xs := [1,2,3,4]
for x in xs[2..]
    say "$x"
    xs.insert(10*x)

say "$xs"
fail unless "$xs" == "[1, 2, 3, 4, 20, 30, 40]"

// Don't need to test tables, they work, but you may run into recently inserted keys