[Haskell-cafe] Proposal: Pragma EXPORT

[Ivan Lazar Miljenovic]

On 17 September 2013 09:35, Evan Laforge <qdunkan at gmail.com> wrote:
> On Mon, Sep 16, 2013 at 4:09 PM, Wvv <vitea3v at rambler.ru> wrote:
>> I suggest to add instead of (or with) export section Pragma EXPORT:
>
> I doubt this has much chance, since haskell already made its choice
> here a long time ago (and even if it were still up for discussion,
> PRAGMA isn't right for it), but this brings up a design question I've
> had.
>
> I too prefer to declare visibility on the declaration rather than in a
> separate list.  C doesn't really have a proper module system, but
> header files are effectively a separate module signature.  C++ and
> Java and go preferred to mark visibility on the declaration.  The ML
> family keeps visibility and declarations separate, which is where I
> assume haskell got it (that or maybe modula?).  In the case of the
> MLs, though, it's a much more developed concept, since they have
> module signatures and functors and all that.
>
> In light of haskell's very basic module system, is there any
> particular philosophical reason to prefer a separate export list?  Or
> are those who prefer it for practical reasons?  The only thing I can
> think of is that it provides a nice summary of the module, which
> haddock capitalizes on.  But when I want a summary, I look at haddock,
> which would already be capable of hiding internal definitions.  I have
> heard that haskell's module system was originally intended as a kind
> of simple-as-possible placeholder (like records... cough cough), maybe
> the designers though an ML-style module system might eventually
> materialize?
>
> To me it's always been a hassle to have to jump to the top of the file
> and fiddle with the export list, so much so that I tend to leave it
> off until a module is pretty stabilized.  It can also be confusing
> when the export list is in a different order from the declarations.
> Sometimes I want to explicitly mark something private, and simply
> "doesn't happen to be in the export list" is too implicit, so I wind
> up putting a _ on it.
>
> None of this is a big deal, but I'm curious about other's opinions on
> it.  Are there strengths to the separate export list that I'm missing?

I do like the actual "summary" aspect as you've noted, as I can at
times be looking through the actual code rather than haddock
documentation when exploring new code (or even trying to remember what
I wrote in old code).

It also makes actual definitions cleaner/shorter rather than
cluttering them with extra annotations (either PRAGMAs or
public/private markers), though this is not that big of a deal.

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-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com