How do you assign a global var in a CAS function?

[webmasterpdx]

I did figure this out...

EXPORT MMM:=256;

#cas
TEST(l):=
BEGIN
RETURN MMM*l[3];
END
#end

...but MMM is a Home variable when done this way.
Let's say I want to create a global CAS list, which can be indexed using []. How do I do that from a CAS program?