Re-exporting namespaces (was: Re: Packages and modules)

[Malcolm Wallace]

Simon Marlow <simonmarhaskell at gmail.com> wrote:

> So I don't like this idea of re-exporting namespaces.  Here's why.
> 
> When I see 'import M', I have to search not only the filesystem, but 
> also for possible namespaces re-exported by *all* the other import 
> declarations in the file, which means I have to understand all those 
> other import declarations, and the process is recursive.

True.  But I don't see how it is much different from ordinary imports:
if an entity e is used in the source text, but not defined there, you
must search the modules that are imported to see where e was defined.
In general, e might not be explicitly defined in /any/ of the
directly-imported modules, so you must recursively check their
imports/re-exports.

> If this is hard for the compiler, it's hard for the user too.  Someone
> understanding your source code has a lot of places to look to find the
> target of an import.

I think it is rather easy for the compiler actually.  Agreed that it
provides a slight extra burden on the human reader.  But I don't think
it is significantly larger than the current burden of knowing the
definition site of a function.

> I believe there should be a clean separation between
>    - constructing the global module namespace, and
>    - interpreting the source code of a module

OK, but that is in direct conflict with the original proposal (to
specify a package alongside a module import), which abandons the idea of
a "global" module namespace!  Indeed, the whole motivation was that we
_don't_ want a global module namespace, because that would require all
modules in all packages to have unique names.

> that is, mapping an import declaration to a module should require 
> nothing more than searching the filesystem and package database.  This
> is true now, and I think we should ensure it remains true, for the 
> benefit of tool and language implementors.

At the moment, the compiler must search the filesystem, package
database, and *interface files* (for imports/re-exports).  With explicit
namespaces, nothing changes there (except that namespaces must also be
recorded in the interface files).

Regards,
    Malcolm