[shawn_w]

You're not using `integer` in the perl example like you're supposed to. Try

    perl -Minteger -E 'say ~-0'

and it should work as expected.

[omoikane]

That is true, but for the kind of code where I might use this trick, there usually aren't enough `~-$x` for `use integer;` to be worthwhile, I would just do `($x-1)` instead.