Aliasing current module qualifier

[Iavor Diatchki]

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 at 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 at gmail.com>
> wrote:
>
>> On Mon, Sep 29, 2014 at 4:19 AM, Herbert Valerio Riedel <hvr at 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 ...
>>
>> --
>> brandon s allbery kf8nh                               sine nomine
>> associates
>> allbery.b at gmail.com
>> ballbery at sinenomine.net
>> unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
>>
>> _______________________________________________
>> Glasgow-haskell-users mailing list
>> Glasgow-haskell-users at haskell.org
>> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>>
>>
>
>
> --
> John Meacham - http://notanumber.net/
>
> _______________________________________________
> ghc-devs mailing list
> ghc-devs at haskell.org
> http://www.haskell.org/mailman/listinfo/ghc-devs
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/ghc-devs/attachments/20140930/a4930eb0/attachment.html>