[Haskell] Data.Generics.gzip3 anyone?
David Fox
ddssff at gmail.com
Mon Jun 1 19:35:35 EDT 2009
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
>
Oh, thank goodness!
-david
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