On the theory that a List is just a Capture that happens to contain
only positionals, I'd say Lists should try to behave like Arrays
when used as one. The only counterargument would be if it forces
unnecessary mutation of otherwise immutable values, but that doesn't
seem to be required for readonl
The draft Synopsis 29 [*] shows that the .keys, .kv, .pairs,
and .values methods are defined for Array but not List.
[*] http://svn.pugscode.org/pugs/docs/Perl6/Spec/Functions.pod
However, t/spec/S29-array/kv.t has entries like:
# (1,).kv works correctly
{
my @a = ();
@a
