[[Introduce the notion of "idiom".]]

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[[idiom for procs with optional leading arguments, followed by fixed later arguments]

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Idiomatic use of [foreach] in place of [lassign].

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[vwait] forever

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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''
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bind . <F2> {console show}



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The whole area of event programming: [Event programming and why it is relevant to Tcl/Tk programming]


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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.


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[Meta Programming] collects together several distinct, if related, idioms.




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[static variables]








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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
      } 












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Also see [Nat Pryce]'s "Tcl Programming Idioms" [http://www.doc.ic.ac.uk/~np2/patterns/tcl/index.html].






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[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 [http://www.man.ac.uk/~zzcgudf/tcl/repeat.tcl] 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
        }











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[[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 ...]]




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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



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    if 0 {
    Stuff
    }
is an alternative [comment] mechanism.
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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]."
    }
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Several people [http://groups.google.com/groups?ic=1&th=d9ede905e2422e6b] have thought about the not-all-root-names-are-OK-for-your-widget-tree quirk.




















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[Arts and crafts of Tcl-Tk programming]