note and hush for #22

protolude.cabal

@@ -46,6 +46,7 @@ library
     Functor
     Semiring
     Bifunctor
+    Exceptions
     Panic
 
   other-modules:

src/Exceptions.hs

@@ -0,0 +1,28 @@
+{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+
+module Exceptions (
+  hush,
+  note,
+  tryIO,
+) where
+
+import Base (IO)
+import Data.Function ((.))
+import Control.Monad.Trans (liftIO)
+import Control.Monad.IO.Class (MonadIO)
+import Control.Monad.Except (ExceptT(..), MonadError, throwError)
+import Control.Exception as Exception
+import Control.Applicative
+import Data.Maybe (Maybe, maybe)
+import Data.Either (Either(..))
+
+hush :: Alternative m => Either e a -> m a
+hush (Left _)  = empty
+hush (Right x) = pure x
+
+note :: (MonadError e m) => e -> Maybe a -> m a
+note err = maybe (throwError err) pure
+
+tryIO :: MonadIO m => IO a -> ExceptT IOException m a
+tryIO = ExceptT . liftIO . Exception.try

src/Protolude.hs

@@ -35,6 +35,7 @@ import Either as X
 import Applicative as X
 import Conv as X
 import Panic as X
+import Exceptions as X
 
 import Base as Base hiding (
     putStr           -- Overriden by Show.putStr