LambdaCase, why not

download-sdmf/Main.hs

 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 
 module Main where
 
@@ -23,16 +24,16 @@ main =
         =<< ( runExceptT $
                 do
                     [announcementPath, readCap] <- lift getArgs
-                    -- Parse read capability
-                    cap <- mightFail "Failed to parse capability: " . pure . parse pCapability "<argv>" . T.pack $ readCap
 
                     -- Load server announcements
                     announcements <- mightFail "Failed to parse announcements: " $ decodeFileEither announcementPath
 
-                    case cap of
-                        (SDMFVerifier _) -> ExceptT . pure . Left . Failed $ "Nothing implemented for verifier capabilities."
-                        (SDMFWriter rwcap) -> go announcements (writerReader rwcap)
-                        (SDMFReader rocap) -> go announcements rocap
+                    -- Parse read capability
+                    (mightFail "Failed to parse capability: " . pure . parse pCapability "<argv>" . T.pack) readCap
+                        >>= \case
+                            SDMFVerifier _ -> ExceptT . pure . Left . Failed $ "Nothing implemented for verifier capabilities."
+                            SDMFWriter rwcap -> go announcements (writerReader rwcap)
+                            SDMFReader rocap -> go announcements rocap
             )
   where
     go :: Announcements -> Reader -> ExceptT Failed IO BL.ByteString