Why don't they just use `tailcall`? That would make it's obvious what it's doing because we've been using the term for nearly half a century, and the entire literature on the subject uses the term "tail call".

Even better would be to just automatically insert a tail call - like every other language that has supported tail calls for decades - provided the callee has the same signature as the caller. If it's undesirable because we want a stack trace, then instead have some keyword or attribute to suppress the tail call - such as `no_tail`, `nontail` or `donttail`.

Requiring tail calls to be marked will basically mean the optimization will be underutilized. Other than having a stack trace for debugging, there's basically no reason not to have the optimization on by default.