I haven’t seen units and signatures used much — is there a particular reason for that?

Good idea in theory, not so great in practice. :slightly_smiling_face:

Generic interfaces turned out to be a more convenient approach?

A more serious answer is that macros that expand to run-time bindings are much easier to write in a world where you don’t separate interface and implementation.

So, we still use units in some places (DrRacket puts them to good use), but the level of generality and abstractions that units provide do not pay off most of the time.

That makes sense. Thanks for the info!

Also units were developed before/in parallel with the module system, and the additional benefits that units provide (recursive modules and multiple instantiation) are not significant enough, since you can get away with mutation and functions