'''It's not.''' It used to be, but it's not now, with Tcl interpreters after 8.0. [[Refer to objective evidence.]] It is necessary to answer the question, though, because so many antique claims to that effect continue to circulate. ---- Tcl is often somewhat slower than Perl for comparable operations. Algorithms that match Perl's regular expressions well generally favor Perl, sometimes by a large factor; a lot of work has gone into optimizing Perl's REs. On the other hand, Perl REs sometimes are only a ''thousandth'' as fast as Tcl's, and, in one very public case [http://shootout.alioth.debian.org/gp4/benchmark.php?test=regexdna&lang=all], Tcl is over four times as fast as Perl on a comparable RE chore. Lambda-the-ultimate briefly discusses how this can be true [http://lambda-the-ultimate.org/node/2064]. ---- [[Explain other penalties--correct Unicode and thread handling, ...]] ---- Naive Tcl coders rarely understand the simple steps that boost [Tcl performance]. [[Explain why this affects Tcl differentially.]] ---- See http://www.equi4.com/md5/ for one example where Tcl is not that much slower. Perhaps [JCW] will update these tests to reflect the new md5 code... ---- [Arjen Markus] From my own experience I can add that Perl and Tcl may have different ideas about what seems the same task. For instance: reading a file line by line. I noticed in a slightly naive test that Tcl would convert the end-of-line sequence, and Perl would not. (Note: I have not delved into the details and it may be specific to the particular releases I used then). This means that setting up a performance test requires a thorough understanding of what each language will do. Furthermore, slight changes in the implementation of the algorithms may make all the difference. (Somewhere I see apples and pears lurking behind shrubberies of intricacies!) ---- [DKF] - Just noting here that 8.4 is the fastest Tcl to date, even faster than 8.0, as listed in [Tcl Benchmarks]. Despite having i18n and thread support... ---- [Setok] - The topic isn't even true for straightforward examples. I converted the Perl intro available at http://www.altparty.org/archive/invi.pl direct to Tcl 8.4 and it was faster (there is also a more optimised version at http://www.altparty.org/archive/invi.tcl). ---- Tcl's not that slow compared to Perl: http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=tcl&lang2=perl ---- [Category Advocacy] - [Category Performance]