[Haskell-cafe] Support of multi-constructor types by UNPACK pragma

[Johan Tibell]

GHC doesn't unpack sums, like B in the example.


On Sun, Jun 15, 2014 at 10:30 PM, Carter Schonwald <
carter.schonwald at gmail.com> wrote:

> Are you sure that's not supported? That seems like a bug if so.  I'm away
> from my computer right now so I can't check.
>
> What ghc version? How are you checking if the unpack is firing?
>
> Ghc 7.8 should by default be unpacking ALL strict small fields.
>
>
> On Sunday, June 15, 2014, Nikita Volkov <nikita.y.volkov at mail.ru> wrote:
>
>> Currently the pragma only supports single-constructor types. So in the
>> following example it will simply be ignored:
>>
>> data A =
>>   A1 Char |
>>   A2 {-# UNPACK #-} !B
>>
>> data B =
>>   B1 Int |
>>   B2 Bool
>>
>> However it seems to be easily solvable by changing the type A to
>> something like the following during unpacking:
>>
>> data A =
>>   A1 Char |
>>   A2_1 Int |    -- from B1
>>   A2_2 Bool     -- from B2
>>
>> Am I missing something? Why is it not implemented?
>> ​
>>
>>
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