[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
  
  }
  
  demo

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[MG] 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.

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[Category Example]