Updated 2015-11-07 00:30:06 by pooryorick

namespace unknown overrides ::unknown for a given namespace.

Synopsis  edit

namespace unknown ?script?

Attributes  edit

from Tcl version

Documentation  edit

TIP 181

See Also  edit

Locally-scoped command aliases are fun!
Use namespace unknown to look up commands in a list of dictionaries.

Another let unknown know  edit

NEM 2006-11-13: Here is an updated version of let unknown know that makes use of the 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 }

rwm 2010-03-12: The above code will not correctly return error codes from the 'known' function. (IMHO: I note that the 8.5 catch/error/return and the new unknown are not well explained especially return -options) I made the following changes to correct it:
old --> set rc [catch { uplevel 1 [linsert $args 0 ::apply $handler] } result]
new --> set rc [catch { uplevel 1 [linsert $args 0 ::apply $handler] } result opts]
old --> return -code $rc $result
new --> return -options $opts $result