Piers Cawley wrote:

>  Here's a rubyish idiom:
>  
>    my &old_behaviour := &function;
>  
>    &function := sub { try_some_stuff || &old_behaviour }
>  
>  Except, with binding it doesn't work like that, you end up with an infinite
>  loop. 

But this version *should* work correctly:

     # Bind the name '&old_behaviour' to the closure that is currently bound to
     # the name '&function'...
     my &old_behaviour := &function;

     # Rebind the name '&function' to the specified closure, calling the
     # old behaviour (via its new name) if necessary...
     &function := sub { try_some_stuff || old_behaviour(*@_) };

No infinite loop involved.

Perl 6 even has specific syntactic sugar for this kind of thing:

     &function.wrap( { try_some_stuff || call(*@_) } );

See: http://dev.perl.org/perl6/doc/design/syn/S06.html#Wrapping

Damian