[Haskell-beginners] Tagged types

[PICCA Frederic-Emmanuel]

I endup with this solution, whcih is for me quite elegant. Maybe this could be generalize with the singleton package.

mkSomeDataCollection :: DataCollection a b -> SomeDataCollection
mkSomeDataCollection c = withSCollectType $ \s -> 
                                       withSCollectSourceFormat $ \f ->
                                         SomeDataCollection s f (coerce c)
    where
      withSCollectType :: (forall c. SCollectType c -> SomeDataCollection) -> SomeDataCollection
      withSCollectType cont = if "ref-" `isPrefixOf` imagePrefix c
                              then cont SCaracterization
                              else cont SCollect

      withSCollectSourceFormat :: (forall c .SCollectSourceFormat c -> SomeDataCollection) -> SomeDataCollection
      withSCollectSourceFormat cont = case imageSuffix c of
                                        (Just "cbf") -> cont SCbf
                                        (Just "h5") -> cont SHdf5
                                        (Just _) -> cont SCbf
                                        Nothing -> cont SCbf


I can not use singleton since I decided to stick to Debian stable/unstable

Cheers and thanks a lot for the help.

Frederic