Multiple return values I'm not very interested in. Lily has first-class tuples, and you can return a tuple which I might later add in desugaring for. But multiple return values themselves cause a lot of problems with the internals being pretty set on 0 or 1 return.

Macros are a hard no. DSLs, maybe. For the latter, I could see allowing a pluggable import handler through Lily's options. But I'm reluctant to commit to a yes or no on that at the moment, since I'd rather get over the hump of api not being fully fleshed out.

Really glad to hear that about multiple return values. In my mind multiple return values are a solution for the problem of "oh, we haven't invented pattern matching yet", and matching against tuples is soooo much cleaner and more consistent.

Didn't realize about tuples, thanks for info! Are they typechecked on length?

Out of curiosity, can I ask for your reasons about macros, if you have them fleshed out enough? Not really sure what you mean by "pluggable import handler" in this context, though. Tx!