[Haskell-beginners] Tagged types

[PICCA Frederic-Emmanuel]

Hello, So I end-up for now with two singletons for my SomeDataCollection

So I red the Datacollection from an xml file (col) then I create the SomeDataCollection type depending on a bunch of values found in the Datacollection.
like this.

                       return $ if "ref-" `isPrefixOf` imagePrefix col
                                then case imageSuffix col of
                                     (Just "cbf") -> SomeDataCollection SCaracterization SCbf (coerce col)
                                     (Just "h5") -> SomeDataCollection SCaracterization SHdf5 (coerce col)
                                     (Just _) -> SomeDataCollection SCaracterization SCbf (coerce col)
                                     Nothing -> SomeDataCollection SCaracterization SCbf (coerce col)
                                else case imageSuffix col of
                                     (Just "cbf") -> SomeDataCollection SCollect SCbf (coerce col)
                                     (Just "h5") -> SomeDataCollection SCollect SHdf5 (coerce col)
                                     (Just _) -> SomeDataCollection SCollect SCbf (coerce col)
                                     Nothing -> SomeDataCollection SCollect SCbf (coerce col)


Now I would like to do something like

                       let t = if "ref-" `isPrefixOf` imagePrefix col
                               then SCaracterization
                               else SCollect

and then

                       return SomeDatacollection t f (coerce col)

But If I try to do this I have an error like this


src/ISPyB/Soap.hs:119:37-44: error:
    • Couldn't match type ‘'Collect’ with ‘'Caracterization’
      Expected type: SCollectType 'Caracterization
        Actual type: SCollectType 'Collect
    • In the expression: SCollect
      In the expression:
        if "ref-" `isPrefixOf` imagePrefix col then
            SCaracterization
        else
            SCollect
      In an equation for ‘t’:
          t = if "ref-" `isPrefixOf` imagePrefix col then
                  SCaracterization
              else
                  SCollect

how can I fix this and make the code better to read.

thanks

Fred