Tail call FSM

[arrdem]

Tail calls of F can be famously rewritten into a GOTO as mentioned in #11. Another property of the tail call structure is that for f and g mutually tail recursive f and g can be rewritten into a finite state machine h such that when f returns (apply g x) this is simply a bytecode jump with no stack operations rather than being a stack call.

Such FSM transformation is valid if and only f and g (and potentially more functions) form a call graph clique where mutual calls occur only from the tail position. Mutually recursive calls not in the tail position cannot be rewritten as such.

Honestly I don't think a whole lot of Clojure code is structured such that this would be a valuable transform, but it would be interesting to build the requisite call graph clique analysis and see if that is in fact the case.