modern Tcl and correct quoting

[Poor Yorick]

On Wed, Jun 12, 2013 at 10:18:54PM +0000, Poor Yorick wrote:
> 
> Putting [expr] arguments in braces can result in much better performance as it
> allows Tcl to cache a byte-coded version of the expression.  It can also avoid unintended processing that might occur via double substitution.  Ref http://wiki.tcl.tk/10225.  
> 
> [eval] concatenates its arguments and passes them through the interpreter again
> to be parsed and executed as a script.  This results in double substitution.
> Here's an example from the patch:
> 

Another point about [eval] and braces is that passing it a single braced
argument rather than multiple arguments can result in a dramatic performance
gain due to bytecode caching and execution.  This can be true also for [expr],
[if], and [while]:

Here's an example:

% info patchlevel
8.6.0
% time {eval incr i} 10000
2.374413 microseconds per iteration
% time {eval {incr i}} 10000
0.6567845 microseconds per iteration


-- 
Yorick