error_handler : unique "caller ID" ?

Dear list, a penny for your thoughts on the following problem. Does anyone have an idea how to find a unique "caller ID" for a user-defined error handler ? The goal is to get a cached error messages tree where the following snippet would yield an array as below it: // start-of-snippet function Outer(&$a) { trigger_error('entering Outer'); $a=Inner($a) ; trigger_error('leaving Outer') ; } function Inner($x) { trigger_error('entering Inner'); return(2*$x) ; } trigger_error('Here we go '); $b = 1 ; $b = Outer($b) ; trigger_error('End result is $b'); // end-of-snippet Output: Array( [0] => 'Here we go' ['Outer(<unique_ID_01>)'] => Array( [0] => 'entering Outer' ; ['Inner(<unique_ID_02>)'] => Array(

      [0] => 'entering Inner' ;
       )

[1] => 'leaving Outer' ; ) [1] => 'End result is 2' ) I've considered the 'args' option in debug_backtrace(), but that fails for referenced arguments. Having read access to a variable's address (like a C-pointer) would be perfect - but Google tells me you can't in PHP. Any other idea's ? Regards, Bert