[Introduce the notion of "idiom".]
[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
The whole area of event programming [L1 ].
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.