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There was an effort, in 2012, to create a generalized TCO in Clojure using CPS and trampolining. I don't remember why it wasn't fully pursued, but the JVM team is now talking about eventually fixing the core issue behind not supporting tail calls.

Clojure Conj 2012: http://youtu.be/RLqqGSthmC0

Source: https://github.com/cjfrisz/clojure-tco

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I experimented with this too. It doesn't work out because you need to know at fn definition time and at the call site that you're using a non-standard calling convention. You can't rewrite all functions without a substantial performance overhead, so you need to be selective. Scala has a compiler plugin for type-directed CPS, but you have to annotate the crap out of your functions and things break down in a bad way for generic higher-order functions. If you wanted to take a real run at this in Clojure, you'd have to compile two versions of every function: the usual `invoke` methods plus an `invokeCPS` method with compiler-inserted call-site trampolining code. Then the programmer would still be saddled with ^:cps metadata or similar.

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