On Jan 21, 2008, at 9:08 AM, Peter Michaux wrote: >> Proper tails calls are not an optimization; they certainly do change >> semantics, insofar as you can't write certain programs without them >> being guaranteed. > > I've been trying to find out how they are not an optimization. I > haven't read anyone else that thinks they are not an optimization but > I have read other people refer to them as an optimization.
Read more, then :-/. The Scheme and Pre-Scheme histories are interesting (in Pre-Scheme you used GOTO for a tail call -- explicit syntax I favor for ES4). See, for instance, Anton van Straaten's fine comment in the same LtU post I cited: http://lambda-the-ultimate.org/node/472#comment-3568 and especially: http://lambda-the-ultimate.org/node/472#comment-3549 Quote: "The ironic thing is that we're talking about a bug whose presence in the language implementation, and in people's minds, makes it difficult to detect that it is a bug. They don't think it's a bug, because they "know" recursion is unnatural and even dangerous — but the only reason they "know" that, is because their language implementation has a bug which makes it so. It's a recursive bug, which is particularly difficult to detect when one makes a habit of avoiding recursion..." > I think > that from an application programmers point of view they are an > optimization since the same program will run without proper tail calls > if the computer has infinite resources. And if my mother had wheels, she'd be a trolley-car. Meanwhile, back in reality, no computer has infinite resources, and as you pointed out to Igor, making "TCO" an option makes it useless on the web -- browsers have different, or no, stack quotas or redzoning. Semantics are not about the meanings of programs assuming infinite resources. > Following one of those links leads to a wiki and the wiki has the > following page which discusses proper tail calls as an optimization in > the language > > http://c2.com/cgi/wiki?TailCallOptimization Yes, it' s a common TLA but citing one use of it doesn't settle the debate. Please read more. /be _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
