Re: Use "range," not "for"?
From: Glenn Jackman (xx087_at_freenet.carleton.ca)
Date: 02/13/04
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Date: 13 Feb 2004 01:10:24 GMT
David McClamrock <mcclamrock@locl.net> wrote:
> I've found that a simple "foreach" loop fairly often won't do the jobs I
> want done,
Really? Why?
[...]
> 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 "$i. \"range\" is beautiful!"}
>
> Or, if you have a list called "lum," instead of writing this:
> for {set i 0} {$i < [llength $lum]} {incr i} {puts [lindex $lum $i]}
> you can write this:
> range i 0 no [llength $lum] {puts [lindex $lum $i]}
>
> To go backward, skipping every other number, instead of this:
> for {set i 10} {$i >= 0} {incr i -2} {puts $i}
> you can write this:
> range i 10 to 0 -2 {puts $i}
[...]
Woof, it looks needlessly complicated. You don't have to muck about
with uplevel at all. Have a look at http://wiki.tcl.tk/10795
It demonstrates an "integer range generator" proc called [..]
Using it would change your examples to:
1 foreach i [.. 1 10] {puts "$i. '..' is beautiful"}
2 foreach i [.. 0 [expr {[llength $lum] - 1}]] {puts [lindex $lum $i}
# OK, that's not as pretty as your [range], but it's a crummy
# example anyway
3 foreach i [.. 10 0 -2] {puts $i}
Here's a wiki page showing a "do ... until ..." loop, which demonstrates
how to neatly handle executing a script body that's passed as an
argument to a proc:
http://wiki.tcl.tk/917
-- Glenn Jackman NCF Sysadmin glennj@ncf.ca
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