[Richard Suchenwirth] 2007-04-26 - A little fun project while waiting for a lengthy build: the following code produces a string with the calendar of one month (as a subset of what the Unix command of same name does), e.g.
 % cal April 2007
     April 2007
 Su Mo Tu We Th Fr Sa
  1  2  3  4  5  6  7
  8  9 10 11 12 13 14
 15 16 17 18 19 20 21
 22 23 24 25 26 27 28
 29 30

Here's the code, densely textured :^)

 proc cal {{month {}} {year {}}} {
    if {$month eq ""} {set month [clock format [clock sec] -format %B]}
    if {[llength $month] > 1} {
      set res {}
      foreach m $month {
        append res [cal $m $year]\n\n
      }
      return [string trimright $res]
    }
    if {$year eq ""}  {set year [clock format [clock sec] -format %Y]}
    set res "     $month $year\n Su Mo Tu We Th Fr Sa\n"
    set weekday [clock format [clock scan "1 $month $year"] -format %w]
    append res  [string repeat "   " $weekday]
    scan [clock format [clock scan "1 $month $year"] -format %m] %d decm
    set maxd [numberofdays $decm $year]
    for {set d 1} {$d <= $maxd} {incr d} {
	append res [format %3d $d]
	if {[incr weekday]>6} {append res \n; set weekday 0}
    }
    set res
 }
 proc numberofdays {month year} {
    if {$month==12} {set month 1; incr year}
    clock format [clock scan "[incr month]/1/$year  1 day ago"] \
	-format %d
 }
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Someone else might want to take a look at the above code and add the appropriate localisation/internationalizations (so that the day and month names are displayed in the local language preferences, etc.
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[wdb] simply great!
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[MJ] - Added that if the month is a list of month names, the result will be a calender for all the months (e.g. [[cal {Apr May}]])
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[Category Date and Time]