bar

#! /usr/bin/env perl6

v6;
sub MAIN() {
    use lib './ext/xyz/bin';
    use xyz <foo>;
    my $foo = foo();
    say "Testy says: $foo!";
}

ext--xyz--bin--xyz.pm

#! /usr/bin/env perl6

v6;

sub foo() is export {
    return "lalala";
}

sub MAIN(*@foo) {
    say "Testy says: ", foo(), @foo;
}

output

[11:09:44] &2 $ perl6-m bar
===SORRY!===
Error while importing from 'xyz': no EXPORT sub, but you provided positional argument in the 'use' statement