[Haskell-cafe] mtlx has a nice design but is slow

[Mark Snyder]

I'm the author for mtlx, and admittedly I didn't do anything about efficiency when I implemented it.  Is there any initial place I ought to look for tips on inlining? I'll start with the pragmas page (http://www.haskell.org/ghc/docs/7.0.3/html/users_guide/pragmas.html) I suppose.  I'm happy for any suggestions--optimizing hasn't been one of my focuses, so it's time for me to learn I suppose!

I did switch to newtype definitions in the most recent version (0.1.5), which probably helped a lot compared to data definitions, but there are no inline pragmas in use, so perhaps there are some good opportunities for optimization.

~Mark Snyder

>
>Is the package missing some obvious inlining in the instances?
>
>> I just refactored my type and transform system prototype (introduced in [1]
>> but changed since then) from using mtlx [2] (type-indexed monad transformers
>> described in [3]) to mtl using RWST. mtlx allowed me to cleanly separate the
>> various monadic components in a convenient way. Unfortunately, I found it to
>> be too slow. The refactoring was an experiment to see how slow. I was rather
>> surprised:
>>
>> Running time of a compiled main with a list of tests:
>> ? mtlx (7 transformers): 2 min 52 sec
>> ? mtl (RWST): 0 min 13 sec
>>
>> It's frustrating to see such a huge performance gap for a better design.
>>
>> Regards,
>> Sean
>>


      
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