A new feature in Tcl 8.5 that extends the [unknown] mechanism to be customisable on a per-[namespace] basis. See TIP 181 for details [http://www.tcl.tk/cgi-bin/tct/tip/181]. ---- [NEM] ''13 Nov 2006'': Here is an updated version of [let unknown know] that makes use of 8.5 features: ''namespace unknown'' and [apply]. While (much) longer than the original version, each "known" snippet can have its own parameters, with all the usual forms accepted by [proc] (i.e., defaults, [args]). Wrapping of new functionality is essentially completely transparent, and each new known thing executes as an independent proc, without adding new command names. You can delegate to the next unknown handler by calling ''next'' (or returning a [continue] exception). Without arguments, ''next'' will invoke the next handler with the original command line, otherwise it will pass the rewritten form. proc know {params body} { set ns [uplevel 1 { namespace current }] set old [namespace eval $ns { namespace unknown }] set new [list $params $body $ns] namespace eval $ns [list namespace unknown [list ::known $new $old]] } proc known {handler old args} { set rc [catch { uplevel 1 [linsert $args 0 ::apply $handler] } result] if {$rc == 4} { # continue - invoke next handler if {[llength $result] == 0} { uplevel 1 $old $args } else { uplevel 1 $old $result } } else { return -code $rc $result } } proc next args { return -code continue -level 2 $args } Examples of use: # expand leading word know {cmd args} { if {[llength $cmd] > 1} { uplevel 1 $cmd $args } else { next } } # numeric ranges proc range {from to} { set ret [list] while {$from <= $to} { lappend ret $from; incr from } return $ret } know {args} { if {[regexp {^([0-9]+)\.\.([0-9]+)$} $args -> from to]} { range $from $to } else { next } } ---- [[ [Category Command] ]]