[JM] Nov 7th 2010, This little toy resembles the key rings that contains a "perpetual calendar", of course we can create such calendar with [clock] commands, but this time, the objective was to re-create the mechanical shifts of labels on such key rings.
you can add more years to this little toy as long as you add them in groups of 7.
<<br>>On the other hand, it was a good excuse to play with lists and grid commands.


   * You have to align the year with the month using the buttons < and >
   * For leap years (which are marked with an asterisk) make sure you use the month with a yellow highlight

[perpetualCalSS]

the screenshot above shows the november 2010 calendar, where I underlined today's date 11/28, sunday.

 #console show

 set wkDays [list lun mar mie jue vie sab dom]

 set years [list 2018 2017 2016* ---- 2015 2014 2013\
 2012* ---- 2011 2010 2009 2008* ----\
 2007 2006 2005 2004* ---- 2003 2002\
 2001 2000* ---- 1999 1998 1997 1996*\
 ---- 1995 1994  1993 1992* ---- 1991\
 1990  1989 1988* ---- 1987  1986  1985\
 1984* ---- 1983  1982  1981  1980* ----\
 1979  1978  1977  1976* ----  1975  1974\
 1973  1972* ----  1971  1970  1969  1968*]

 proc refresh {wkDays years} {
 foreach widget {.lblUno .lblDos .lblTres .lblCuatro .lblCinco .lblSeis .lblSiete} valor $wkDays {
        $widget configure -text $valor
 }

 foreach widget {.yr1 .yr2 .yr3 .yr4 .yr5 .yr6 .yr7} valor [lrange $years 0 6] {
        $widget configure -text $valor
 }
 }

 proc shift3 {_L} {
 upvar 1 $_L L 
 set L [concat [lindex $L end] [lrange $L 0 end-1]]
 }

 proc shift4 {_L} {
 upvar 1 $_L L 
 set L [concat [lrange $L 1 end] [lindex $L 0]]
 puts $L
 }

 proc shift> {} {
 global wkDays years
 shift3 years
 shift4 wkDays

 refresh $wkDays $years
 }

 proc shift< {} {
 global wkDays years
 shift3 wkDays
 shift4 years
 refresh $wkDays $years
 }

 label .title -text "Calendario Perpetuo"
 grid .title -columnspan 9

 button .btn> -text ">" -command shift>
 button .btn< -text "<" -command shift<

 for {set i 1} {$i < 8} {incr i} {
 label .yr$i -text "1234"
 }
 grid .btn< .yr1 .yr2 .yr3 .yr4 .yr5 .yr6 .yr7 .btn>

 foreach month {Ene Feb Mar Abr May Jun Jul Ago Sep Oct Nov Dic} {
 label .lbl$month -text $month
 }

 label .lblEneB -text "Ene" -bg yellow
 label .lblFebB -text "Feb" -bg yellow
 grid  x .lblEne .lblMay .lblAgo  .lblMar .lblJun .lblDic .lblJul
 grid  x .lblOct x       .lblFebB .lblFeb x       .lblSep .lblAbr
 grid  x x       x       x        .lblNov x       x       .lblEneB

 for {set i 1} {$i < 32} {incr i} {
 label .lbl$i -text "$i"
 }

 foreach dia {Uno Dos Tres Cuatro Cinco Seis Siete} {
 label .lbl$dia -text $dia
 }
 grid x .lblUno .lblDos .lblTres .lblCuatro .lblCinco .lblSeis .lblSiete

 grid x .lbl1 .lbl2 .lbl3 .lbl4 .lbl5 .lbl6 .lbl7
 grid x .lbl8 .lbl9 .lbl10 .lbl11 .lbl12 .lbl13 .lbl14
 grid x .lbl15 .lbl16 .lbl17 .lbl18 .lbl19 .lbl20 .lbl21
 grid x .lbl22 .lbl23 .lbl24 .lbl25 .lbl26 .lbl27 .lbl28
 grid x .lbl29 .lbl30 .lbl31

 for {set i 0} {$i < 9} {incr i} {
 grid columnconfigure . $i -minsize 50
 }

 refresh $wkDays $years


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