[WJG] (16/Feb/06) A simple proc to compare the contents of two lists. It returns a list equal to the differences.

 #----------------
 # compare list a with b
 #----------------
 proc listcomp {a b} {
  foreach i $a {
    if {[lsearch -exact $b $i]==-1} {
      lappend diff $i
    }
  }
  return $diff
 }

 set a {1 2 3 4 5 6}
 set b {2 4 6 8}

 puts "list a = $a\nlist b = $b\nThe difference between a and b is [listcomp $a $b]."