empty_interface.m:005: Warning: the interface of module `empty_interface' does
empty_interface.m:005:   not export anything.
empty_interface.m:005:   To be useful, a module should export something. A file
empty_interface.m:005:   should contain at least one declaration other than
empty_interface.m:005:   `:- import_module' in its interface section(s). This
empty_interface.m:005:   would normally be a `:- pred' or `:- func'
empty_interface.m:005:   declaration, or a `:- type', `:- inst', `:- mode',
empty_interface.m:005:   `:- typeclass' or `:- instance' definition.