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Comment by otto-edgar | Hacker News Reader

I think TCO and JVM are orthogonal discussions -- by the time the bytecode is generated, the TCO may have already been performed.

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I'm actually not sure about that. I think the Javascript compiler target also lacks full TCO. The Idris 2 compiler itself I think does not perform this optimization, because the Scheme reference backend does it already. I might be wrong about that, but I remember several active unresolved discussions on this topic in the community last year. I haven't been involved actively in it for several months, so my memory might be wrong.

The javascript back end handles mutually recursive tail calls. It finds connected components and rewrites them to use a trampoline-like thing. There is a nice explanation of how it works at the top of the file:

https://github.com/idris-lang/Idris2/blob/main/src/Compiler/...

One could argue that it's not "full" TCO, but it does cover a lot of use-cases. That rewrites to NamedCExp, so it could be reused by other backends.

The Java backend seems to be doing its own thing. There aren't a lot of comments or documentation in that repository, but I do see evidence that it's doing something interesting in src/Compiler/Jvm/Optimizer.idr:

    Pure $ if shouldTrampoline && hasNonSelfTailCall tailCallCategory
      then trampolineExpression True inlinedAndTailRecursionMarkedExpr
      else inlinedAndTailRecursionMarkedExpr

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