[PD] optional argument in abstraction

[marius schebella]

hi,
I want to create an abstraction that can take an optional symbol as 
argument.
if there is a symbol argument then use this, if not then use a default 
symbol.

for example
[my_print hello_world!]
would print "hello_world!"

[my_print]
(without argument) would print "default_text"

[my_print 0] or [my_print 123] would also print "default_text".

I tried all variations of route, select, list trim, but could not get it 
to work. maybe I forgot something. or maybe there is another trick. I am 
using 0.40.
marius.