Aliasing current module qualifier

Iavor Diatchki iavor.diatchki at
Tue Sep 30 12:18:06 UTC 2014


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", ) 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'?

 On Sep 29, 2014 11:02 PM, "John Meacham" <john at> 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>
> wrote:
>> On Mon, Sep 29, 2014 at 4:19 AM, Herbert Valerio Riedel <hvr at>
>> 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
>> ballbery at
>> unix, openafs, kerberos, infrastructure, xmonad
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> --
> John Meacham -
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