Add a few more stackable traits that extend IntQueue.

Incrementing's put adds 1 to whatever value is put.
Filtering's put only puts non-negative values.

All together, these two traits as well as Doubling can be combined
in various ways to yield different kinds of behavior for each
permutation of mixins (and the mixin order is very relevant, due
to how trait linearization works).

With just a little bit of code you can achieve such power and
flexibility.