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1+{-# LANGUAGE FlexibleInstances #-}
2+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
3+{- |
4+Module : Data.SemiIsoFunctor.Wrapped
5+Description : SemiIso instances for wrapped monads.
6+Copyright : (c) Paweł Nowak
7+License : MIT
8+
9+Maintainer : Paweł Nowak <pawel834@gmail.com>
10+Stability : experimental
11+
12+Every monad (with fail) is a SemiIsoMonad.
13+-}
14+module Data.SemiIsoFunctor.Wrapped where
15+
16+import Control.Applicative
17+import Control.Lens.SemiIso
18+import Control.Monad
19+import Data.SemiIsoFunctor
20+
21+-- | A wrapped covariant functor.
22+newtype WrappedCovariant m a = WrappedCovariant { runCovariant :: m a }
23+ deriving (Functor, Applicative, Alternative, Monad)
24+
25+instance Monad m => SemiIsoFunctor (WrappedCovariant m) where
26+ simapCo ai m = m >>= either fail return . apply ai
27+
28+instance Monad m => SemiIsoApply (WrappedCovariant m) where
29+ sipure ai = either fail return (unapply ai ())
30+ f /*/ g = liftM2 (,) f g
31+
32+instance (Monad m, Alternative m) => SemiIsoAlternative (WrappedCovariant m) where
33+ siempty = empty
34+ f /|/ g = f <|> g
35+
36+instance Monad m => SemiIsoMonad (WrappedCovariant m) where
37+ f //= g = f >>= (\x -> g x >>= \y -> return (x, y))