Constrained generic parameters are actually super useful.
> If exceptions are encoded in function's interface, then they have to be in ABI
They already are in Itanium
> you cannot serialize the communication using some protocol with a fixed number of types (eg. JSON and friends), because now you need to account for the infinite variety of exception types.
No, the only exception that arises is ser/deserialization error. You can also trivially represent an error in JSON using an object, which is exactly what JSON RPC protocols do. It's also never safe to throw across an FFI boundary and similarly nonsensical to throw across a serialization boundary, so I'm not sure why you'd care.
