I can't find any mention of if they provide a C-compatible ABI. Kinda useless as a systems language if they don't - you can't call it from anything else.
Perhaps I scanned too quickly. I probably missed since there is no actual mention of ABI (or e.g. which calling conventions it supports on what platforms). The page is confusing - it seems to discuss ABI and syntax and stuff, which isn't exactly related to "compatability" afaict.
I digress... just the usual problems with wiki-type sites.
It compiles to LLVM and LLVM abstracts the calling convention. So it might be safe to assume it supports all the calling conventions that LLVM supports.
Sure, but that requires knowledge of how LLVM works. Some dude checking out the language probably doesn't.