The addparent opcode doesn't work currently with PMCs (on either end):
harmony:~/Projects/parrot mdiep$ cat test.pir
.sub main @MAIN
$P0 = newclass "Foo"
$P1 = getclass "String"
addparent $P0, $P1
harmony:~/Projects/parrot mdiep$ parrot test.pir
Parent isn't a ParrotClass
You can, however, use the subclass opcode to subclass a PMC in PIR.
This should either be implemented or the documentation should make
note of the behavior. Note also that it wasn't particularly clear (to
me as a Parrot user) that a ParrotClass is a PIR-defined class.