You can use F# with WASM. I know F# convert recursive tail calls to loops but I understand this is another case. But shouldn't F# have the same problem?
I have not been following WASM generally, but my understanding after reading this:
Unlike regular machine language, WASM does not allow you to control the call semantics. That is, if you emit x86 machine instructions you can handle TCE entirely in your own compiler, the machine itself does not care.
WASM has special call instructions, these perform basically a conventional stack frame/call stack approach and you can't short circuit it. The closest you can get, which works fine for auto-recursive functions and maybe some detectable mutually recursive functions, is to convert tail calls into loops within the compiled WASM output. So recursive tail calls work fine in WASM if your compiler doesn't turn them into calls, but leaves them as a self-implemented (by the compiler) loop structure using whatever appropriate WASM instructions are available. This is fine for auto-recursive functions, but puts the burden at implementing TCE for them on the compiler writer. Which means you'll get it for some languages that compile to WASM, but not all. And only for the limited cases they support (probably restricted to auto-recursive and some mutual recursive circumstances).
What this proposal introduces is a new version of the call instruction that would be used in tail call positions. Then the WASM interpreters would do the work of actually combining the stack frames internally. Detecting that a call is a tail call is actually pretty straightforward for a compiler. Given that it is a tail call, it can emit (or not) the new call instruction and will get TCE "for free". It doesn't have to do a code transformation from recursive to looping, and it can be applied more broadly than just recursive circumstances.
F# compiles to CIL bytecode, which has a tail call instruction. I'm not sure what happens to that when CIL is compiled to wasm, but since there's no way to do a general translation, it probably just drops the tail part and makes it a regular call.
Self recursion is a special case that WASM backend targets can more or less efficiently resolve the same way a human can convert a recursive function into a non-recursive one: explicitly put arguments onto your own simulation of a stack and perform the computation in a loop.
Unfortunately self recursion is only a subset of tail calling.
