My-Fourth-Modules-Script.pm6

#!/usr/bin/env perl6

proto MAIN($) is export { * }

package My-Fourth-Modules-Script {

  multi MAIN($x) {
    say "This is the inside MAIN called with $x";
  }
}

# multi sub MAIN($x) {
#    say "This is the outer MAIN called with $x";
#    My-Second-Modules-Script::MAIN($x);
# }

# $ ./My-Fourth-Modules-Script.pm6
# No usage information could be determined
# $ ./My-Fourth-Modules-Script.pm6 32
# No usage information could be determined

My-Modules-Script.pm6

#!/usr/bin/env perl6

module My-Modules-Script {
  sub MAIN($x) { # Note that `is export` here makes no change in behavior
    say "This is the inside MAIN called with $x";
  }
}

sub MAIN($x) {
  say "This is the outer MAIN called with $x";
  My-Modules-Script::MAIN($x);
}

My-Second-Modules-Script.pm6

#!/usr/bin/env perl6

module My-Second-Modules-Script {
  sub NOT-MAIN($x) is export {
    say "This is the inside MAIN called with $x";
  }
}

sub MAIN($x) {
  say "This is the outer MAIN called with $x";
  My-Second-Modules-Script::NOT-MAIN($x);
}
# Output:
# % ./My-Second-Modules-Script.pm6
# Usage:
#   ./My-Second-Modules-Script.pm6 <x>
# % ./My-Second-Modules-Script.pm6 42
# This is the outer MAIN called with 42
# Could not find symbol '&NOT-MAIN'
#   in sub MAIN at ./My-Second-Modules-Script.pm6 line 11
#   in block <unit> at ./My-Second-Modules-Script.pm6 line 3

My-Third-Modules-Script.pm6

#!/usr/bin/env perl6

proto MAIN($) is export { ... }

module My-Third-Modules-Script {
  multi MAIN($x) {
    say "This is the inside MAIN called with $x";
  }
}

multi sub MAIN($x) {
   say "This is the outer MAIN called with $x";
   My-Second-Modules-Script::NOT-MAIN($x);
}

# % ./My-Third-Modules-Script.pm6 32
# Stub code executed
# in sub MAIN at ./My-Third-Modules-Script.pm6 line 3
# in block <unit> at ./My-Third-Modules-Script.pm6 line 5

# % ./My-Third-Modules-Script.pm6
# Usage:
#   ./My-Third-Modules-Script.pm6 <x>

output.console

% ./My-Modules-Script.pm6
Usage:
  ./My-Modules-Script.pm6 <x>
% ./My-Modules-Script.pm6 42
This is the outer MAIN called with 42
No such method 'MAIN' for invocant of type 'My-Modules-Script'
  in sub MAIN at ./My-Modules-Script.pm6 line 11
  in block <unit> at ./My-Modules-Script.pm6 line 3