On Thu, Nov 20, 2008 at 11:57 PM, David Roundy <[EMAIL PROTECTED]> wrote:
> On Thu, Nov 20, 2008 at 02:44:33AM +0300, Dmitry Kurochkin wrote:
>> hunk ./src/Darcs/Patch/Real.hs 175
>> >                                                a:>p':>b ->
>> >                                                    do (b',xs') <- mac b xs 
>> > goneby
>> >                                                       --traceDoc 
>> > (greenText "foo1" $$
>> > -                                                     --          
>> > showPatch (sort_coalesceFL $
>> > -                                                     --                   
>> >   effect $ p':<:a)) $ Just ()
>> > -                                                     NilFL <- return $ 
>> > sort_coalesceFL $ effect $ p':<:a
>> > +                                                     --          
>> > showPatch (sort_coalesce_effects $ p':<:a)) $ Just ()
>> > +                                                     NilFL <- return $ 
>> > sort_coalesce_effects $ p':<:a
>> >                                                       return (reverseRL 
>> > (p':<:a)+>+b', xs')
>> >                                                     `mplus` do NilFL <- 
>> > return goneby
>>
>> Use sort_coalesce_effects instead of sort_coalesceFL.
>>
>> It would be easier to read if "sort_coalesce_effects $ p':<:a" is
>> bound to a name with let. Not sure if it worth changing though.
>
> But alas, that would cause ghc's brain to explode.  NilFL is a GADT,
> and you can't use let bindings with GADT patterns.  This relates to
> the fact that matching NilFL puts a constraint on the type witnesses,
> and because let bindings are lazy, they don't work well with that.

I did not know that. Thanks for the explanation!

Regards,
  Dmitry

>
> David
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