<div dir="ltr">Wow, very informative. I read somewhere that Python prevented infinite loops, but performing this in IDLE on my office Windows box proved me wrong: while 1: print "Hi" Thomas Allen <div class="gmail_quote">2008/9/8 Alaric Snell-Pym <<a href="mailto:alaric@snell-pym.org.uk">alaric@snell-pym.org.uk</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 <div class="Ih2E3d"> On 8 Sep 2008, at 2:23 pm, Thomas Allen wrote: > I know that Python can tell if a loop is infinite, although I'm not > sure if that behavior applies to Regex (and I can't test it -- I > couldn't write an infinite search if required...but if you provide > one, I will). What I mean is that there may be something of > interest in their source. </div>It's not infinity that's necessarily the problem; the problem is that it's possible to write a regexp that takes millions of years to decide. Which isn't infinite, but is a long time to wait for dinner. And you can't reliably tell if a loop is infinite. Any automated test, except in very restricted languages (non Turing-complete ones), can only classify loops (or any other bit of code into) these three categories: - Will loop forever - Won't loop forever (but might loop for a billion years) - Might loop forever; who knows? ...and most samples will fall into the latter category, which tells you no more than you already knew ;-) What makes you say that Python can tell if a loop is infinite, out of interest? I'm sure it must be a misinterpretation of something, unless the halting problem has been solved while I wasn't looking... <a href="http://en.wikipedia.org/wiki/Halting_problem" target="_blank">http://en.wikipedia.org/wiki/Halting_problem</a> "In computability theory, the halting problem is a decision problem which can be stated as follows: given a description of a program and a finite input, decide whether the program finishes running or will run forever, given that input. Alan Turing proved in 1936 that a general algorithm to solve the halting problem for all possible program-input pairs cannot exist." ABS - -- Alaric Snell-Pym Work: <a href="http://www.snell-systems.co.uk/" target="_blank">http://www.snell-systems.co.uk/</a> Play: <a href="http://www.snell-pym.org.uk/alaric/" target="_blank">http://www.snell-pym.org.uk/alaric/</a> Blog: <a href="http://www.snell-pym.org.uk/?author=4" target="_blank">http://www.snell-pym.org.uk/?author=4</a> -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (Darwin) iEYEARECAAYFAkjFMq4ACgkQRgz/WHNxCGqy4wCZAdUt2dQXBJrvWZerZ4cdO520 XDIAnjWhygjTS5QnvNQ8M5aOuvoFq+Fm =hObQ -----END PGP SIGNATURE----- <div><div></div><div class="Wj3C7c"> _______________________________________________ textmate mailing list <a href="mailto:textmate@lists.macromates.com">textmate@lists.macromates.com</a> <a href="http://lists.macromates.com/listinfo/textmate" target="_blank">http://lists.macromates.com/listinfo/textmate</a> </div></div></blockquote></div> </div>