PMCs ("Parrot Magic Cookies")

PMC registers are handles to objects in Parrot’s built-in object system:

new $P0, 'Integer'
assign $P0, 3
set $P1, $P0
assign $P1, 4
print $P0         # outputs "4"

Built-in PMC types include:

Integer     Array          NameSpace    Sub
Float       Hash           Class        Coroutine
String      Iterator       Object       Continuation
Complex     FileHandle     Role         Exception