Re: Use "range," not "for"?

From: Bryan Oakley (bryan_at_bitmover.com)
Date: 02/13/04 

Date: Fri, 13 Feb 2004 01:20:00 GMT

David McClamrock wrote:
> Thanks to everyone who suggested ways to get a proc to recognize all
> variables in the global scope--here's why I wanted to know. (Maybe someone
> has done this better already--if so, don't hesitate to let me know!)
>
> I've found that a simple "foreach" loop fairly often won't do the jobs I
> want done, and I need to use "for"--ugh! Well, I recently read at least
> part of a book about Python. It didn't look like an improvement over Tcl
> for the most part, but it has at least a few good features, one of which is
> the "range" expression. I thought a "range" procedure in Tcl might be a
> good substitute for the clumsy "for." So, here's my first effort. Instead
> of writing this:
>
> for {set i 1} {$i<= 10} {incr i} {puts "$i. \"for\" is ugly!"}
>
> you can write this:
>
> range i 1 to 10 {puts "$i. \"range\" is beautiful!"}

Using globals is not the right solution. Your range code simply won't
work inside a procedure. Try running this code:

proc foo {} {
     set j "Hello, world"
     range i 1 to 10 {
         puts "$i: $j"
     }
}

You'll instantly see the problem. Instead of using global variables you
need to use upvar and "uplevel 1".

Also, the very first uplevel "uplevel #0 proc ..." really doesn't do
anything. What do you think it does? If you can explain what you are
trying to accomplish we can tell you a better way to accomplish it. If
you're trying to force the definition of range into the global scope
it's better to fully qualify the name, ie: "proc ::range".

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