overlapping instances in 7.10.1

[Sergei Meshveliani]

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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> 
> 
> 
> 
> 
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