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copied!<p>As you say, tail recursion is a special case of a tail call. Consequently, any language that implements general TCO trivially is "properly tail recursive".</p> <p>The inverse, however, does not hold. There are quite a few languages that only optimise tail recursion, because that is significantly easier -- you can translate it away into a loop directly, and don't need a specific "tail call" operation that manipulates the stack in new ways. For example, that is the reason why languages compiling to the JVM, which doesn't have a tail call instruction, typically only optimise tail (self) recursion. (There are techniques to work around the lack of such an instruction, e.g. trampolines, but they are quite expensive.)</p> <p>Full tail call optimization does not only apply to self (or mutually) recursive calls, but to <em>any</em> calls in tail position. In particular, it extends to calls whose target is <em>not statically known</em>, e.g. when invoking a first-class function or a dynamically-dispatched method! Consequently, it requires somewhat more elaborate (though well-known) implementation techniques.</p> <p>Many functional programming techniques -- but also some popular OO patterns (see e.g. <a href="http://www.ccs.neu.edu/home/matthias/Presentations/ecoop2004.pdf" rel="noreferrer">Felleisen's ECOOP'04 presentation</a> or <a href="http://www.eighty-twenty.org/index.cgi/tech/oo-tail-calls-20111001.html" rel="noreferrer">Guy Steele's blog post</a>) -- require full TCO to actually be usable.</p>

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