one of the documented procedures in this installation of the ACS
ad_decode   args
What it does:
this procedure is analogus to sql decode procedure. first parameter is the value we want to decode. this parameter is followed by a list of pairs where first element in the pair is convert from value and second element is convert to value. last value is default value, which will be returned in the case convert from values matches the given value to be decoded
Defined in: /web/philip/packages/acs-core/utilities-procs.tcl

Source code:

    set num_args [llength $args]
    set input_value [lindex $args 0]

    set counter 1

    while { $counter < [expr $num_args - 2] } {
	lappend from_list [lindex $args $counter]
	incr counter
	lappend to_list [lindex $args $counter]
	incr counter

    set default_value [lindex $args $counter]

    if { $counter < 2 } {
	return $default_value

    set index [lsearch -exact $from_list $input_value]
    if { $index < 0 } {
	return $default_value
    } else {
	return [lindex $to_list $index]