[Haskell] Data.Generics.gzip3 anyone?
David Fox
ddssff at gmail.com
Sat Aug 8 19:09:11 EDT 2009
On Sat, Aug 8, 2009 at 4:05 PM, David Fox <ddssff at gmail.com> wrote:
> Ok, here is another piece of the three way merging puzzle. The gzip3
> function can do three
> way merging when there are no conflicts that need to be resolved manually.
> When there are
> such conflicts we need a user interface which displays the common ancestor,
> the two alternative
> edits, and provides a place to input the merged result. For this we are
> using a generic
> programming interface to formlets . Formlets are members of class
> Applicative, so we can write
> a function to turn a value into a formlet using a gmapA function (this is
> syb-with-class generics):
>
> type GenericA f ctx = forall a. (Applicative f, Data ctx a) => a -> f a
>
> gmapA :: (Applicative f) => Proxy ctx -> GenericA f ctx -> GenericA f ctx
> gmapA ctx f =
> gfoldl ctx k pure
> where k c x = c <*> (f x)
>
> Then the formlet for a value is created using something like this:
>
> gmapA formletOfProxy (formletOfD dict) x
>
> For three way merging, though, we need to turn three values of the same
> type into a formlet,
> something like a gmap3A function:
>
> gmap3A formletOfProxy (formletOfD dict) ancestor variant1 variant2
I guess this should be a more like this:
gmap3A formletOfProxy (formletOf3WayMergeD dict) ancestor variant1
variant2
when converting a value of an arbitrary algebraic type, and
formletOf3WayMerge would have
custom implementations for various primitive and more specialized types.
>
> Its this gmap3A function that I'm unable to create. I'm hoping someone out
> there will find this
> a piece of cake...
>
>
> On Mon, Jun 1, 2009 at 3:40 PM, Ralf Laemmel <rlaemmel at gmail.com> wrote:
>
>> > Thank you! What I have in mind is three way merging - you have two
>> > revisions based on the same original value, and you need to decide
>> whether
>> > they can be merged automatically or they need to be merged by a user.
>> You
>> > only have a real conflict when both revisions differ from the original
>> and
>> > from each other.
>>
>> Here is the completed exercise.
>> For comparison, the two args versions are shown up-front.
>> There is gzipWithM3 needed for gzip3, and gzip3 itself.
>> I also made it so that the top-level gzip functions have the
>> appropriate polymorphism.
>> Say same type for the args rather than independent polymorphism.
>>
>> {-# LANGUAGE RankNTypes #-}
>>
>> import Prelude hiding (GT)
>> import Data.Generics
>>
>> -- As originally defined: Twin map for transformation
>>
>> gzipWithT2 :: GenericQ (GenericT) -> GenericQ (GenericT)
>> gzipWithT2 f x y = case gmapAccumT perkid funs y of
>> ([], c) -> c
>> _ -> error "gzipWithT2"
>> where
>> perkid a d = (tail a, unGT (head a) d)
>> funs = gmapQ (\k -> GT (f k)) x
>>
>>
>> -- As originally defined: Twin map for transformation
>>
>> gzipWithM2 :: Monad m => GenericQ (GenericM m) -> GenericQ (GenericM m)
>> gzipWithM2 f x y = case gmapAccumM perkid funs y of
>> ([], c) -> c
>> _ -> error "gzipWithM"
>> where
>> perkid a d = (tail a, unGM (head a) d)
>> funs = gmapQ (\k -> GM (f k)) x
>>
>>
>> -- As originally defined: generic zip
>>
>> gzip2 ::
>> (forall x. Data x => x -> x -> Maybe x)
>> -> (forall x. Data x => x -> x -> Maybe x)
>>
>> gzip2 f = gzip2' f'
>> where
>> f' :: GenericQ (GenericM Maybe)
>> f' x y = cast x >>= \x' -> f x' y
>> gzip2' :: GenericQ (GenericM Maybe) -> GenericQ (GenericM Maybe)
>> gzip2' f x y =
>> f x y
>> `orElse`
>> if toConstr x == toConstr y
>> then gzipWithM2 (gzip2' f) x y
>> else Nothing
>>
>>
>> -- For three args now
>>
>> gzipWithT3 ::
>> GenericQ (GenericQ (GenericT))
>> -> GenericQ (GenericQ (GenericT))
>> gzipWithT3 f x y z =
>> case gmapAccumT perkid funs z of
>> ([], c) -> c
>> _ -> error "gzipWithT3"
>> where
>> perkid a d = (tail a, unGT (head a) d)
>> funs = case gmapAccumQ perkid' funs' y of
>> ([], q) -> q
>> _ -> error "gzipWithT3"
>> where
>> perkid' a d = (tail a, unGQ (head a) d)
>> funs' = gmapQ (\k -> (GQ (\k' -> GT (f k k')))) x
>>
>> gzipWithM3 :: Monad m
>> => GenericQ (GenericQ (GenericM m))
>> -> GenericQ (GenericQ (GenericM m))
>> gzipWithM3 f x y z =
>> case gmapAccumM perkid funs z of
>> ([], c) -> c
>> _ -> error "gzipWithM3"
>> where
>> perkid a d = (tail a, unGM (head a) d)
>> funs = case gmapAccumQ perkid' funs' y of
>> ([], q) -> q
>> _ -> error "gzipWithM3"
>> where
>> perkid' a d = (tail a, unGQ (head a) d)
>> funs' = gmapQ (\k -> (GQ (\k' -> GM (f k k')))) x
>>
>> gzip3 ::
>> (forall x. Data x => x -> x -> x -> Maybe x)
>> -> (forall x. Data x => x -> x -> x -> Maybe x)
>>
>> gzip3 f = gzip3' f'
>> where
>> f' :: GenericQ (GenericQ (GenericM Maybe))
>> f' x y z = cast x >>= \x' -> cast y >>= \y' -> f x' y' z
>> gzip3' ::
>> GenericQ (GenericQ (GenericM Maybe))
>> -> GenericQ (GenericQ (GenericM Maybe))
>> gzip3' f x y z =
>> f x y z
>> `orElse`
>> if and [toConstr x == toConstr y, toConstr y == toConstr z]
>> then gzipWithM3 (gzip3' f) x y z
>> else Nothing
>>
>
>
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