Power set

sub powerset(Set $s) { $s.combinations.map(*.Set).Set }
say powerset set <a b c d>;

Output:

set(set(), set(a), set(b), set(c), set(d), set(a, b), set(a, c), set(a, d), set(b, c), set(b, d), set(c, d), set(a, b, c), set(a, b, d), set(a, c, d), set(b, c, d), set(a, b, c, d))

If you don't care about the actual Set type, the .combinations method by itself may be good enough for you:

.say for <a b c d>.combinations

Output:

a
b
c
d
a b
a c
a d
b c
b d
c d
a b c
a b d
a c d
b c d
a b c d