36 lines
982 B
Haskell
36 lines
982 B
Haskell
{-# LANGUAGE GeneralisedNewtypeDeriving #-}
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module Monad(
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App
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,module Control.Monad.Fail
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,module Control.Monad.IO.Class
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,throwE
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,except
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,runApp
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) where
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import qualified Control.Monad.Trans.Except as T
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import Control.Monad.Fail
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import Control.Monad.IO.Class
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-- We need this type isomorphism, because we want a different
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-- MonadFail implementation, if someone knows how to do this
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-- without writing the isomorphism out explicitly for all
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-- the other instances, (or without scary GeneralisedNewtypeDeriving)
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-- I would be happy
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newtype App a = App { runApp' :: T.ExceptT String IO a}
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deriving (Functor, Applicative, Monad, MonadIO)
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instance MonadFail App where
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fail = throwE
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-- reimplementing ExceptT interface
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-- I would love not to have to do this but I don't know how
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throwE :: String -> App a
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throwE = App . T.throwE
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except :: Either String a -> App a
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except = App . T.except
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runApp :: App a -> IO (Either String a)
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runApp = T.runExceptT . runApp'
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