> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Dave Herman > Sent: 21. januar 2008 16:58 > To: Peter Hall > Cc: Brendan Eich; es4-discuss@mozilla.org; Jeff Dyer; Erik Arvidsson > Subject: Re: proper tail calls > > > I am a bit out of my depth in this discussion, but explicit syntax > > feels wrong to me. However, if it's going to be implicit, > it has to be > > completely invisible (aside from the benefits) - developers > are going > > to want their debugging tools to work as before. > > > > Is there a practical approach to recursion counting, that ES4 could > > require, so that Error.getStackTrace() can use it to produce the > > "expected" result? I must admit, It doesn't feel as trivial in my > > head as that sentence reads... > > You can easily circumvent an expression being in tail > position. For example, if EXP is in tail position and you > want it not to be, just wrap it as: > > let (r = EXP) r > > The program behaves the same, except for the fact that EXP is > no longer in tail position, so it cannot perform a tail call.
Of course some implementations would optimize away r, and EXP would be back in tail position. ISTR that the R5RS made a point of saying that an implementation would be allowed to do that, and I think this ought to be true for ES4 too. Ditto, interprocedural analysis and/or inlining may prove that the body of a "try" can't throw an exception, thereby allowing the exception handler to be removed, thereby exposing a possibility for TCO. And so on. Maybe we need a directive for turning off tail calls: please don't goto f(37) --lars _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
