Re: [Haskell] Data.Generics.gzip3 anyone?

1 Jun 2009


      On Mon, Jun 1, 2009 at 12:20 PM, Ralf Laemmel <rlaemmel@gmail.com> wrote:
...
On Mon, Jun 1, 2009 at 8:20 PM, David Fox <david@seereason.com> wrote:
...
Is there a Scrap Your Boilerplate guru out there who could whip up a
three
argument version of gzip for me?
This can be done of course (untested but type-checked code follows).
Left wondering what the scenario might be :-)
Ralf
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
-- 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
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.

-david