My issue isn’t with the module. Static analysis would have to determine all the possible module()/atom() combinations that could arrive at an apply/3 call site to infer the resulting sum type. async/3 would have a similar issue exacerbated by the fact that it would have to correlate which asyncs can end up at each await/2.
Historically adding a static type system to Erlang failed because the typing of the interprocess communication types is non-trivial and async/3/await/2 involves interprocess communication.
