overlapping instances in 7.10.1

[Sumit Sahrawat, Maths & Computing, IIT (BHU)]

[Adding ghc-devs at haskell.org to cc]

On 21 May 2015 at 02:12, Sergei Meshveliani <mechvel at botik.ru> wrote:

> Now, I delete  `OverlappingInstances'  from  docon.cabal
>
> and also from the   $doconCpOpt  options to call  ghc  on
> demotest/Main.hs.
>
> And now the test runs correct in ghc-7.10.1 !
>
> Only it is 1.5 times slower than in  ghc-7.8.2.
> So:
> a) The test intends overlapping instances,
> b) instance overlaps are not declared for  ghc-7.10.1,
> c) this leads to a correct running, but 1.5 times slower.
>
> I do not know of whether this slow down is due to the removed pragma or
> due to other features of  ghc-7.10.1.
>
> And there remains my question about how GHC could help to recall the
> overlapping instance pairs.
>
> Regards,
>
> ------
> Sergei
>
>
>
>
> On Wed, 2015-05-20 at 23:52 +0400, Sergei Meshveliani wrote:
> > Dear GHC developers,
> >
> > Please, test  ghc-7.10.1  on making  docon-2.12
> >
> >   http://www.botik.ru/pub/local/Mechveliani/docon/
> >
> > and running its    demotest/Main
> > (see install.txt).
> >
> >
> > docon-2.12  has been tested under  ghc-7.8.2,
> >
> > and it has
> >                  extensions: ... OverlappingInstances
> > in  docon.cabal.
> >
> > Making with  ghc-7.10.1  issues a warning and advises to set the related
> > pragma individually to each corresponding instance.
> >
> >
> > (1) First, I ignored this warning, and surprisingly, the library has
> > been made.
> >
> > In the  build/  subdirectory there are  .hi and .o  files,
> > and there have newly appeared the  "dyn" files:
> >
> >   Matr0_.dyn_hi Matr0_.dyn_o Matr0_.hi Matr0_.o  ...
> >
> > (I do not know what does it mean "dyn").
> >
> > Then,
> >         > make install
> > reports
> >
> >   runghc Setup.hs install --user
> >   Installing library in
> >
>  /home/mechvel/docon/2.12/docon/source/inst/lib/x86_64-linux-ghc-7.10.1/docon_99cUeE74HI58Sb9XilYAZ2
> >
> >   Registering docon-2.12.1...
> >
> > Instead of the  .a  file,  ls  shows there
> >
> >   docon_99cUeE74HI58Sb9XilYAZ2  docon_JzkSttB1MsX3R5AQ1eIgvC
> >
> > Are these names intended?
> >
> > Then I command
> >
> >   > cd demotest
> >   > ghc $doconCpOpt -O -rtsopts --make Main
> >   > ./Main
> >
> > It is built and runs. But breaks in the middle with a certain reasonable
> > DoCon error message.
> >
> > The DoCon design is so that choosing a different instance among the
> > overlapping ones may change the algorithm, and the computation cost, but
> > still must produce the same result. It must -- unless DoCon has a bug in
> > some of these instances.
> >
> >
> > (2) All right, I need to set  {-# OVERLAPPABLE #-}  individually to each
> > instance which may overlap with some other instance in DoCon.
> >
> > There is declared a great number of instances. And it occurs difficult
> > for me to recall now: which instance does overlap with something and
> > which does not
> > (at least they all worked correct in ghc-7.8.2).
> >
> > Well, I can set  {-# OVERLAPPABLE #-}  to _each_ instance.
> > But such a program does not look nice.
> >
> > And I would like to be more definite and to set  {-# OVERLAPPING #-}  to
> > all appropriate places.
> > Suppose that I forget that some instance overlaps with something and
> > skipped this pragma. The above test shows that this can lead to a wrong
> > program to run
> > (is this feature intended?).
> >
> > And what will be the consequence if  {-# OVERLAPPING #-}  is set to an
> > instance which does not overlap with anything?
> >
> > Can the compiler help to list the overlaps?
> >
> > Please, advise,
> >
> > ------
> > Sergei
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
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> > Glasgow-haskell-users at haskell.org
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> >
>
>
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-- 
Regards

Sumit Sahrawat
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