[Introduce the notion of "idiom".]
Well, when I look up idiom [L1 ] I am uncertain in what vein the term is being used here.
Perhaps as "a style or manner of expression peculiar to a programming language " ?
[idiom for procs with optional leading arguments, followed by fixed later arguments]
Idiomatic use of foreach in place of lassign.
vwait forever
args or argv parsing facilitated through use of arrays such as cmdArs(-linemap). Is this from Brent's book? RS: Yes, at the beginning of the Pane Manager, 2nd ed.p279
bind . <F2> {console show}
The whole area of event programming: Event programming and why it is relevant to Tcl/Tk programming
When you start to think about megawidgets and/or widget subclassing, consider whether creative use of tags is a good Tk solution. In many cases, it's enough to "gang" different elements together with tags.
Meta Programming collects together several distinct, if related, idioms.
An idiom useful for self-testing source fragments and documentation uses is this one, as formulated in a clt posting by DKF:
# Test for running stand-alone *or* in the plugin. Follow an idea
# through to its logical conclusion...
if {[string equal $::argv0 [info script]] || \
[array exists ::embed_args]} {
main
}
Also see Nat Pryce's "Tcl Programming Idioms" [L2 ].
Donal Fellows is good about reporting errors correctly. More precisely, Tcl programmers often knock together handy little control structures (repeat, do while, ...) but frankly leave the error-traceback as a loose end for some indeterminate future clean-up. Donal's repeat example [L3 ] shows how to handle tracebacks cleanly. The heart of it is
global errorInfo
if {[uplevel #0 [list catch $cmd($rid) ::repeat::msg]]} {
append errorInfo "\n (\"repeat\" script)"
bgerror $msg
Stop $rid
return
}
[Explain Miguel's generalization of 32 to bit-length with self-modifying code in Binary representation of numbers as one of several alternatives. regsub-ing a script can be a performance win.] [And there's a class of idioms targeted at Tcl performance, anyway.] [I (Miguel) think that Can you run this benchmark 10 times faster is also a good example ...]
Constants, globals, and so on: reference especially Bob Techentin's post: "One method that many people use is to declare a global array of related data, which you can then reference in your procs with a single global statement. Like this:
array set defaultData {
color red
filetype text
cputime 100
}
proc myProc { } {
global defaultData
if { $defaultData(color) == "green" } {
puts "I can't tell the difference between red and green."
}
}"You can wrap this behavior into a proc, so you don't have to remember to declare the array global all the time:
proc const {key} {set ::defaultData($key)}
...
if {[const color] == "green"} {...} ;#RS
if 0 {
Stuff
}is an alternative comment mechanism.
Although old-timers cheerfully manipulate [info tclversion], $::tcl_version, [info glob exp*] (for Expect), and so on, the modern idiom for retrieving version information is
foreach package {Tcl Expect ...} {
puts "The version is [package provide $package]."
}Several people [L4 ] have thought about the not-all-root-names-are-OK-for-your-widget-tree quirk.
bind . <Up> {exec wish $argv0 &; exit} ;# RS - rapid restart after editsTV I'm not sure what idiom is defined like exactly, but I did a procedure called pro_args which allows you to name and assign value to some of many arguments of a procedure, by naming only the ones you want it will automatically lookup defaults for the others.
So you'd have a procedure lets say newarray:
% info args newarray nx ny bn fs ib ipi jb jpi x y
of which certain arguments have defaults, and you want to make sure x and y get values for instance 100 and 50 respectively. Of course we could then type something like newarray a b c d e ... 100 50, with each argument, also the ones for which we want the default values, filled in or listed. pro_args lets you form such a command by using:
% pro_args newarray {{x 100} {y 50}}
newarray 3 3 array {} {} {} {} {} 100 50And when it looks ok, you use
eval [pro_args newarray {{x 100} {y 50}}]to execute the command, in this case a bwise command to generate an array of blocks.
Maybe eval could be part of the command to save typing. This construction is useful for commands with more than a few or complicated arguments and defaults for them.
Tcl Idioms for Process Management
jcw - To make sure a variable exists (and set it to empty otherwise), you can use lappend:
lappend a
if {$a ne "ok"} { ... }or even:
if {[lappend a] ne "ok"} { ... }Instead of the usual "if {![info exists a]} { set a "" }".
slebetman - surely that should be:
catch {lappend a}unless you don't mind your application unexpectedly exiting or popping up error messages from time to time.
LV I'm curious as to what kind of error you were envisioning? I tried missing and present variable, and array references, and lappend didn't raise any errors there. I even tried this:
set a "{"
llength $a
lappend aand even though llength complains about a having unmatched open brace in the list, lappend didn't complain at all.
slebetman Oh yes it does complain:
% set a {"}
% lappend a x
unmatched open quote in list
% # Even the example you gave above complains:
% set a "{"
% lappend a x
unmatched open brace in list
% info patchlevel
8.4.12what version are you using?
[ Arts and crafts of Tcl-Tk programming - Category Glossary ]