one of the documented procedures in this installation of the ACS
util_memoize   tcl_statement   { oldest_acceptable_value_in_seconds "" }
What it does:
Returns the result of evaluating the Tcl statement argument and then remembers that value in a cache; the memory persists for the specified number of seconds (or until the server is restarted if the second argument is not supplied) or until someone calls util_memoize_flush with the same Tcl statement. Note that this procedure should be used with care because it calls the eval built-in procedure (and therefore an unscrupulous user could
Defined in: /web/philip/packages/acs-core/utilities-procs.tcl

Source code:

    # we look up the statement in the cache to see if it has already
    # been eval'd.  The statement itself is the key

    if { ![nsv_exists util_memoize_cache_value $tcl_statement] || ( ![empty_string_p $oldest_acceptable_value_in_seconds] && ([expr [nsv_get util_memoize_cache_timestamp $tcl_statement] + $oldest_acceptable_value_in_seconds] < [ns_time]) )} {

	# not in the cache already OR the caller spec'd an expiration
	# time and our cached value is too old

	set statement_value [eval $tcl_statement]
	nsv_set util_memoize_cache_value $tcl_statement $statement_value
	# store the time in seconds since 1970
	nsv_set util_memoize_cache_timestamp $tcl_statement [ns_time]

    return [nsv_get util_memoize_cache_value $tcl_statement]