This page is intended to document issues when effective execution of Tcl scripts is targeted. Please add any single topic below as to keep it as a comprehensive list. Append general comments as usual to the end of this page -- [RJM].

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   1. Write [expr] commands with the argument in curly braces whenever possible. This avoids conversion of numbers in strings and back. The speed impact may be a factor of 20 or so.

   2. Do not write procs without Arguments. Empty procs may execute approx. 4 times slower. At least speed critical procs schould be defined with a dummy argument. To be ''precise'' (according to comment of [MS]), procs without arguments are NOT the problem, only invocations without trailing character after command name. So invoke commands without arguments preferably as '''command;''' (trailing semicolon) as long as the bug is not fixed.

   3. ...

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[RJM]: Referencing to (2) I can say that I found this by accident. On a Win98 machine with 266 MHz clock, the following execution times apply:

An empty proc without Arguments:
 % proc test {} {}
 % time {test} 1000
 95 microseconds per iteration

An empty proc with an Argument:
 % proc fast {x} {}
 % time {fast 5} 1000
 12 microseconds per iteration

I performed several variations, also with filled body and so on. The crucial differencs lies in defining a proc with or without an argument.
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[MSW]: Actually calling a proc without an argument.
For comparison:
 % time {test} 1000
 12 microseconds per iteration
 % time {fast 5} 1000
 3 microseconds per iteration
 % proc maybe {{empty {}}} {}
 % time {maybe} 1000
 13 microseconds per iteration
 % time {maybe empty} 1000
 3 microseconds per iteration
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[MS] This is Bug #458361 [https://sourceforge.net/tracker/?func=detail&aid=458361&group_id=10894&atid=110894], but the interpretation is wrong: it is not ''proc calls without arguments'' that are slow, but rather ''scripts that consist of a single word and whose string equals a command name'' - which significantly reduces the likelihood of hitting the bug. Even adding a space to the script destroys the effect. Witness
 %  proc maybe {{empty {}}} {}
 % # call with argument
 % time {maybe empty} 10000  
 4 microseconds per iteration
 % # call without argument
 % time {maybe} 10000
 19 microseconds per iteration
 % # call without argument; space added
 %  time {maybe } 10000
 3 microseconds per iteration
 % # call without argument; semicolon added
 % time {maybe;} 10000
 4 microseconds per iteration
 % complex script, call with arguments
 % time {maybe empty; maybe empty} 10000
 7 microseconds per iteration
 % # complex script, call without arguments
 % time {maybe;maybe} 10000
 7 microseconds per iteration
Thanks, I have updated the issue list above accordingly --[RJM]

Hmmm ... not sure about the update; thinking about how to revise it. --[MS]