We already can create sub-circuit but it seems we cannot make sub-circuits using other sub-circuits. I don't know if it is a bug or a feature not yet implemented.
I tried to implement a logical 'full-adder' with an intermediate 'half-adder' as presented in the 'Code' book. I manage to create an 'half-adder' but the 'full-adder' doesn't wok with the sub-circuits 'half-adder'.

It will be very useful to add those sub-circuits in a library for future use. Currently iCircuit is very buggy when loading higher level circuit it fails at loading lower level ones. I also don't know where iCircuit is loading sub-circuits on OS X. Maybe you could on OS X specify the external library directory?

We cannot resize sub-circuit which sometimes makes the schema messy.

To sum up:
- I want to be able to resize sub-circuits in order to make my schema tidy and clean.
- I want to import a sub-circuit in a library for future use and in order to import use created sub-circuits.
- I want to specify a directory on OS X where sub-circuits will be automatically fetched and imported in the library.
- I want to create hierarchy (nested) of sub-circuits in order to create complex high level circuits.

I would like to teach basic logic gates composition to students and I miss all those features to do so.