WJG(17/April/2006) It's often useful to keep lists of unique items but those lists need to be of fixed length. Adding a new item to the list, means that the oldest item has to be deleted: a 'recent documents' list for example. Here's a simple solution. Indeed, it's so simple that the comments are longer than the code itself!
#---------------
# lshift.tcl
#---------------
proc lshift {l i} {
# if the item already exists, just return the list back
if {![lsearch $l $i]} {return $l}
# insert new item at the top
set l [linsert $l 0 $i]
# delete the one at the end
return [lrange $l 0 end-1]
}
#---------------
# the ubiquitous demo
#---------------
proc demo {} {
# just for the linux users
catch {console show}
# create a list
foreach a {apple pear bannana} {
lappend fruit $a
}
# the list before changes
puts $fruit
# cherry will be added, bannana will go
set fruit [lshift $fruit cherry]
puts $fruit
# we already have cherry, no change
set fruit [lshift $fruit cherry]
puts $fruit
}
demoMG Apr 17 2006 - Did you know you can use lrange $list 0 end-1 to trim the last element from the list, and avoid the expr? A couple of suggestions, too: it might be better if you could specify a maximum length instead (recent document/history lists won't always be fully populated, and the user may clear it). Also, if an item is already in the list, it could be better to bring it to the beginning, rather than do nothing.
WJG(17/April/2006) Following your comment, I have changed the lrange statement as you suggested. The overall list length; well, that could be adjusted by simply adding a new items to the list elsewhere. The suggestion about swapping is a good one. After all, if a file is to be re-loaded, it usually is the last one worked on.
WJG(17/April/2006) So, here we go. Here's a more complete example. Using the comments made by MG.
# recentfiles.tcl
#---------------
# keep our values private
#---------------
namespace eval recent {
set cmd puts ;# default command called in menu
set max 5 ;# maximum of 5 files in the list
# build list to hold filenames
for {set i 1} {$i<=$max} {incr i} {
lappend files "--"
}
}
#---------------
# update menu
#---------------
proc recent:update {mnu fname} {
# recreate the menu
destroy $mnu
menu $mnu -tearoff 0
# make changes
# 1) to the file list
set recent::files [lshift $recent::files $fname]
# 2) to the appropriate menu
set i 1
foreach n $recent::files {
$mnu add command -label "$i) $n" -command "$recent::cmd $n"
incr i
}
}
#---------------
# lshift.tcl
# http://wiki.tcl.tk/15758
#---------------
proc lshift {l i} {
# if the item already exists, just return the list back
set swap [lsearch $l $i]
if {$swap!=-1} {
set tmp [lindex $l $swap]
# delete the old location
set l [lreplace $l $swap $swap]
# bring it to the front
set l [linsert $l 0 $i]
return $l
}
# insert new item at the top
set l [linsert $l 0 $i]
# delete the one at the end
return [lrange $l 0 end-1]
}
#---------------
# the ubiquitous demo
#---------------
proc demo {} {
catch {console show}
menu .menu
. configure -menu .menu
menu .menu.file -tearoff 0
.menu add cascade -menu .menu.file -label File
.menu.file add command -label New.. -command fileNew
.menu.file add command -label Open.. -command fileOpen
.menu.file add cascade -label "Recent Documents" -menu .menu.file.recent
.menu.file add separator
.menu.file add command -label "Save As.." -command fileSave
.menu.file add command -label Save -command fileSave
.menu.file add separator
.menu.file add command -label Exit -command fileExit
recent:update .menu.file.recent apple
recent:update .menu.file.recent bannana
recent:update .menu.file.recent cherry
recent:update .menu.file.recent damson
recent:update .menu.file.recent elder
recent:update .menu.file.recent fig
recent:update .menu.file.recent damson ;# this one should have no effect
recent:update .menu.file.recent grapefruit
recent:update .menu.file.recent fig ;# this one, too, should have no effect
}
#---------------
# the ubiquitous demo!
#---------------
demo