Hello, In fact I do not understand this error message, and thus I do not understand how to fix this ? How Can I give hint to ghc in order to fix this compilation error. thanks for your help. Frederic src/XdsMe.hs:214:31-52: error: • Could not deduce (Control.Monad.Reader.Class.MonadReader Beamline IO) 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:183:30-37 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:183:39-43 • In the second argument of ‘($)’, namely ‘toRuchePath attachment’ In a stmt of a 'do' block: attachment' <- liftIO $ toRuchePath attachment In the expression: do { need [toFilePath xml]; container <- liftIO . fromFile . toFilePath $ xml; let attachment = _autoProcProgramAttachment . _autoProcProgramContainer $ container; attachment' <- liftIO $ toRuchePath attachment; .... } Here the signature of the function xdsme' :: SomeDataCollection -> Maybe Cell -> Maybe SpaceGroup -> GZiped -> [Path Abs File] -> ReaderT Beamline IO () xdsme' c@(SomeDataCollection SCollect SHdf5 _) cell sg z is = do