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Cool, now ABCL can have TCO!

This isn't a _general_ tail call optimization--just tail recursion. The issue is that this won't support mutual tail recursion.

e.g.:

(defun func-a (x) (func-b (- x 34)) (defun func-b (x) (cond ((<= 0 x) x) ('t (func-a (-x 3))))

Because func-a and func-b are different (JVM) functions, you'd need an inter-procedural goto (i.e. a tail call) in order to natively implement this.

As an alternative, some implementations will use a trampoline. func-a and func-b return a _value_ which says what function to call (and what arguments) for the next step of the computation. The trampoline then calls the appropriate function. Because func-a and func-b _return_ instead of actually calling their sibling, the stack depth is always constant, and the trampoline takes care of the dispatch.

Sounds like a manual form of clojures recur function.

https://clojuredocs.org/clojure.core/recur

Clojure's loop/recur is specifically tail recursion like scala's tailrec or the optimization described in the blogpost. It doesn't use trampolines to enable tail calls that aren't tail recursion.

Finally.

The ANTLR guys went through terrible contortions for their parsers.

Never felt like working those details out for ABCL.

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