Recently on comp.lang.tcl, Tom Wilkason wrote: "... Incidentally, for backwards compatibility you can have lset for older tcl versions with the following code run during script processing:"

 proc K {a b} {set a}
 if {[string equal [info command lset] {}]} {
   proc lset {listName index val} {
       upvar $listName list
       set list [lreplace [K $list [set list {}]] $index $index $val]
   }
 } ;# end if