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|
-----------------------------------------------------------------------------
-- |
-- Module : Control.Monad.Identity
-- Copyright : (c) Andy Gill 2001,
-- (c) Oregon Graduate Institute of Science and Technology, 2001
-- License : BSD-style (see the file libraries/core/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : portable
--
-- The Identity monad.
--
-- Inspired by the paper
-- /Functional Programming with Overloading and
-- Higher-Order Polymorphism/,
-- Mark P Jones (<http://www.cse.ogi.edu/~mpj>)
-- Advanced School of Functional Programming, 1995.
--
-----------------------------------------------------------------------------
module Control.Monad.Identity (
Identity(..),
runIdentity,
module Control.Monad,
module Control.Monad.Fix,
) where
import Prelude
import Control.Monad
import Control.Monad.Fix
-- ---------------------------------------------------------------------------
-- Identity wrapper
--
-- Abstraction for wrapping up a object.
-- If you have an monadic function, say:
--
-- example :: Int -> IdentityMonad Int
-- example x = return (x*x)
--
-- you can "run" it, using
--
-- Main> runIdentity (example 42)
-- 1764 :: Int
newtype Identity a = Identity { runIdentity :: a }
-- ---------------------------------------------------------------------------
-- Identity instances for Functor and Monad
instance Functor Identity where
fmap f m = Identity (f (runIdentity m))
instance Monad Identity where
return a = Identity a
m >>= k = k (runIdentity m)
instance MonadFix Identity where
mfix f = Identity (fix (runIdentity . f))
|
