Re: [Haskell-beginners] MonadThrow, MonadReader and shake

15 Dec 2018

      Hello,

The` toRuchePath` function has the following constraints on `m`: 
`MonadReader Beamline m, MonadThrow m`

In your code, `m ~ Action` (from Shake) which doesn't fulfil the 
constraints (hence the error).

If you use `liftIO` as suggested (possible because Action has a MonadIO 
instance), `m ~ IO` which doesn't fulfil the constraints (hence the 
other error).

If you want `m ~ ReaderT Beamline m IO`, you can use something like: 
`liftIO $ runReaderT stateBeforeCallingShake $ toRuchePath attachements` 
(you need `stateBeforeCallingShake <- ask` before calling shake).

It should fulfil the constraints because we have instances for 
`MonadThrow IO` and `MonadThrow m => MonadThrow (ReaderT r m)`.

Hope that helps,
Sylvain

On 13/12/2018 10:15, PICCA Frederic-Emmanuel wrote:
...
Hello,
I try to write this sort of code
xdsme' :: SomeDataCollection
        -> Maybe Cell
        -> Maybe SpaceGroup
        -> GZiped
        -> [Path Abs File]
        -> ReaderT Beamline IO ()
xdsme' c@(SomeDataCollection SCollect SHdf5 _) cell sg z is = do
   -- xdsme compute the output path by himself.
   cwd' <- toProcessDataPath c
   rdir <- resultsPrefixFile xdsMePrefix c
   dir <- resultsPrefixDir ("xdsme_" ++ xdsMePrefix) c
   dir' <- resultsPrefixFile "" c
   xmlPath <- parseRelFile $ toFilePath dir' ++ "_xdsme.xml"
   xml <- parseAbsFile $ toFilePath cwd'  toFilePath dir  toFilePath xmlPath
   uploadedPath <- parseRelFile $ toFilePath dir' ++ "_xdsme.uploaded"
   uploaded <- parseAbsFile $ toFilePath cwd'  toFilePath dir  toFilePath uploadedPath
let shakeFiles' = toFilePath cwd'  toFilePath dir  ".shake/"
   let images = getImages c z
liftIO $ shake shakeOptions{ shakeFiles=shakeFiles'
                     , shakeReport=["/tmp/shake.html"]
                     , shakeVerbosity=Diagnostic} $ do
     want [toFilePath uploaded]
-- execute xdsme and deal with input dependencies
     toFilePath xml %> \_out -> do
       need (map toFilePath is)
       processXdsMe cwd' cell sg rdir images
toFilePath uploaded %> \_out -> do
       need [toFilePath xml]
container <- liftIO . fromFile . toFilePath $ xml
-- post processing
       let attachment = _autoProcProgramAttachment . _autoProcProgramContainer $ container
attachment' <- toRuchePath attachment         <- HERE PROBLEM
_ <- copyAttachment' attachment attachment'
let container' = (autoProcProgramContainer . autoProcProgramAttachment .~ attachment') container -- replace attachement
-- upload into ISPYB
       liftIO $ storeAutoProcIntoISPyB c NoAnomalous container'
       cmd_ ("touch" :: String) (toFilePath uploaded)
where
toRuchePath :: (MonadReader Beamline m, MonadThrow m)
             => [AutoProcProgramAttachment WithPrefix]
             -> m [AutoProcProgramAttachment ISPyB]
toRuchePath = mapM go
     where
       go :: (MonadReader Beamline m, MonadThrow m)
          => AutoProcProgramAttachment WithPrefix
          -> m (AutoProcProgramAttachment ISPyB)
       go a = do
         (d, _) <- toPath a
         b <- ask
         newd <- mkText255 . pack . toRuchePath' b . fromAbsDir $ d
         return a {filePath = newd}
but when I try to compile this I get this error.
How can I teach ghc how to solve this issue ?
thanks for your help
Frederic
src/XdsMe.hs:211:22-43: error:
     • Could not deduce (MonadThrow Action)
         arising from a use of ‘toRuchePath’
       from the context: t ~ 'Collect
         bound by a pattern with constructor:
                    SCollect :: SCollectType 'Collect,
                  in an equation for ‘xdsme'’
         at src/XdsMe.hs:180:30-37
       or from: f ~ 'ISPyB.DataCollection.Hdf5
         bound by a pattern with constructor:
                    SHdf5 :: SCollectSourceFormat 'ISPyB.DataCollection.Hdf5,
                  in an equation for ‘xdsme'’
         at src/XdsMe.hs:180:39-43
     • In a stmt of a 'do' block: attachment' <- toRuchePath attachment
       In the expression:
         do { need [toFilePath xml];
              container <- liftIO . fromFile . toFilePath $ xml;
              let attachment
                    = _autoProcProgramAttachment . _autoProcProgramContainer
                      $ container;
              attachment' <- toRuchePath attachment;
              .... }
       In the second argument of ‘(%>)’, namely
         ‘\ _out
            -> do { need [...];
                    container <- liftIO . fromFile . toFilePath $ xml;
                    .... }’
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Re: [Haskell-beginners] MonadThrow, MonadReader and shake

Sylvain Henry