WJG (17/April2006) 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, its 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}
# make a copy of the list with the new item at the top
set j [linsert $l 0 $i]
# return a list equalling the length of the original list sent
set end [expr [llength $l] -1]
return [lrange $j 0 $end]
}
#---------------
# 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