Hello,

What semantics are you using for recursive modules?  As far as I see, if you take a least fixed point semantics (e.g. as described in "A Formal Specification for the Haskell 98 Module System", http://yav.github.io/publications/modules98.pdf ) this program is incorrect as the module does not export anything.

While this may seem a bit counter intuitive at first, this semantics has the benefit of being precise, easily specified, and uniform (e.g it does not require any special treatment of the " current " module).  As an example, consider the following variation of your program, where I just moved the definition in a sperate (still recursive) module:

module A (M.x) where
  import B as M

module B (M.x) where
  import A as M
  x = True

I think that it'd be quite confusing if a single recursive module worked differently then a larger recursive group, but it is not at all obvious why B should export 'x'.  And for those who like this kind of puzzle: what should happen if 'A' also had a definition for 'x'?

Iavor

On Sep 29, 2014 11:02 PM, "John Meacham" <john@repetae.net> wrote:

You don't need a new language construct, what i do is:

     module AnnoyinglyLongModuleName (M.length, M.null) where

    import AnnoyinglongLongModuleName as M

I think ghc would need to be extended a little to make this convienient as it doesn't handle recursive module imports as transparently.

    John

On Mon, Sep 29, 2014 at 8:47 AM, Brandon Allbery <allbery.b@gmail.com> wrote:

On Mon, Sep 29, 2014 at 4:19 AM, Herbert Valerio Riedel <hvr@gnu.org> wrote:

Now it'd be great if I could do the following instead:

    module AnnoyinglyLongModuleName (M.length, M.null) where

    import AnnoyinglyLongModuleName as M -- <- does not work

I think if I wanted this syntax, I'd go for:

    module AnnoyinglyLongModuleName as M where ...

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