2 -- (c) The University of Glasgow 2002-2006
4 -- The IO Monad with an environment
8 IOEnv, -- Instance of Monad
17 -- Getting at the environment
18 getEnv, setEnv, updEnv,
20 runIOEnv, unsafeInterleaveM,
21 tryM, tryAllM, tryMostM, fixM,
24 IORef, newMutVar, readMutVar, writeMutVar, updMutVar
30 import Data.IORef ( IORef, newIORef, readIORef, writeIORef, modifyIORef )
32 import System.IO.Unsafe ( unsafeInterleaveIO )
33 import System.IO ( fixIO )
36 ----------------------------------------------------------------------
37 -- Defining the monad type
38 ----------------------------------------------------------------------
41 newtype IOEnv env a = IOEnv (env -> IO a)
43 unIOEnv :: IOEnv env a -> (env -> IO a)
46 instance Monad (IOEnv m) where
50 fail _ = failM -- Ignore the string
52 instance Applicative (IOEnv m) where
54 IOEnv f <*> IOEnv x = IOEnv (\ env -> f env <*> x env )
56 instance Functor (IOEnv m) where
57 fmap f (IOEnv m) = IOEnv (\ env -> fmap f (m env))
59 returnM :: a -> IOEnv env a
60 returnM a = IOEnv (\ _ -> return a)
62 thenM :: IOEnv env a -> (a -> IOEnv env b) -> IOEnv env b
63 thenM (IOEnv m) f = IOEnv (\ env -> do { r <- m env ;
66 thenM_ :: IOEnv env a -> IOEnv env b -> IOEnv env b
67 thenM_ (IOEnv m) f = IOEnv (\ env -> do { m env ; unIOEnv f env })
70 failM = IOEnv (\ _ -> throwIO IOEnvFailure)
72 failWithM :: String -> IOEnv env a
73 failWithM s = IOEnv (\ _ -> ioError (userError s))
75 data IOEnvFailure = IOEnvFailure
78 instance Show IOEnvFailure where
79 show IOEnvFailure = "IOEnv failure"
81 instance Exception IOEnvFailure
83 ----------------------------------------------------------------------
84 -- Fundmantal combinators specific to the monad
85 ----------------------------------------------------------------------
88 ---------------------------
89 runIOEnv :: env -> IOEnv env a -> IO a
90 runIOEnv env (IOEnv m) = m env
93 ---------------------------
95 -- Aargh! Not inlining fixTc alleviates a space leak problem.
96 -- Normally fixTc is used with a lazy tuple match: if the optimiser is
97 -- shown the definition of fixTc, it occasionally transforms the code
98 -- in such a way that the code generator doesn't spot the selector
101 fixM :: (a -> IOEnv env a) -> IOEnv env a
102 fixM f = IOEnv (\ env -> fixIO (\ r -> unIOEnv (f r) env))
105 ---------------------------
106 tryM :: IOEnv env r -> IOEnv env (Either IOEnvFailure r)
107 -- Reflect UserError exceptions (only) into IOEnv monad
108 -- Other exceptions are not caught; they are simply propagated as exns
110 -- The idea is that errors in the program being compiled will give rise
111 -- to UserErrors. But, say, pattern-match failures in GHC itself should
112 -- not be caught here, else they'll be reported as errors in the program
114 tryM (IOEnv thing) = IOEnv (\ env -> tryIOEnvFailure (thing env))
116 tryIOEnvFailure :: IO a -> IO (Either IOEnvFailure a)
117 tryIOEnvFailure = try
119 -- XXX We shouldn't be catching everything, e.g. timeouts
120 tryAllM :: IOEnv env r -> IOEnv env (Either SomeException r)
121 -- Catch *all* exceptions
122 -- This is used when running a Template-Haskell splice, when
123 -- even a pattern-match failure is a programmer error
124 tryAllM (IOEnv thing) = IOEnv (\ env -> try (thing env))
126 tryMostM :: IOEnv env r -> IOEnv env (Either SomeException r)
127 tryMostM (IOEnv thing) = IOEnv (\ env -> tryMost (thing env))
129 ---------------------------
130 unsafeInterleaveM :: IOEnv env a -> IOEnv env a
131 unsafeInterleaveM (IOEnv m) = IOEnv (\ env -> unsafeInterleaveIO (m env))
134 ----------------------------------------------------------------------
135 -- Accessing input/output
136 ----------------------------------------------------------------------
138 instance MonadIO (IOEnv env) where
139 liftIO io = IOEnv (\ _ -> io)
141 newMutVar :: a -> IOEnv env (IORef a)
142 newMutVar val = liftIO (newIORef val)
144 writeMutVar :: IORef a -> a -> IOEnv env ()
145 writeMutVar var val = liftIO (writeIORef var val)
147 readMutVar :: IORef a -> IOEnv env a
148 readMutVar var = liftIO (readIORef var)
150 updMutVar :: IORef a -> (a -> a) -> IOEnv env ()
151 updMutVar var upd = liftIO (modifyIORef var upd)
154 ----------------------------------------------------------------------
155 -- Accessing the environment
156 ----------------------------------------------------------------------
158 getEnv :: IOEnv env env
159 {-# INLINE getEnv #-}
160 getEnv = IOEnv (\ env -> return env)
162 -- | Perform a computation with a different environment
163 setEnv :: env' -> IOEnv env' a -> IOEnv env a
164 {-# INLINE setEnv #-}
165 setEnv new_env (IOEnv m) = IOEnv (\ _ -> m new_env)
167 -- | Perform a computation with an altered environment
168 updEnv :: (env -> env') -> IOEnv env' a -> IOEnv env a
169 {-# INLINE updEnv #-}
170 updEnv upd (IOEnv m) = IOEnv (\ env -> m (upd env))
173 ----------------------------------------------------------------------
174 -- Standard combinators, but specialised for this monad
176 ----------------------------------------------------------------------
178 -- {-# SPECIALIZE mapM :: (a -> IOEnv env b) -> [a] -> IOEnv env [b] #-}
179 -- {-# SPECIALIZE mapM_ :: (a -> IOEnv env b) -> [a] -> IOEnv env () #-}
180 -- {-# SPECIALIZE mapSndM :: (b -> IOEnv env c) -> [(a,b)] -> IOEnv env [(a,c)] #-}
181 -- {-# SPECIALIZE sequence :: [IOEnv env a] -> IOEnv env [a] #-}
182 -- {-# SPECIALIZE sequence_ :: [IOEnv env a] -> IOEnv env () #-}
183 -- {-# SPECIALIZE foldlM :: (a -> b -> IOEnv env a) -> a -> [b] -> IOEnv env a #-}
184 -- {-# SPECIALIZE foldrM :: (b -> a -> IOEnv env a) -> a -> [b] -> IOEnv env a #-}
185 -- {-# SPECIALIZE mapAndUnzipM :: (a -> IOEnv env (b,c)) -> [a] -> IOEnv env ([b],[c]) #-}
186 -- {-# SPECIALIZE mapAndUnzip3M :: (a -> IOEnv env (b,c,d)) -> [a] -> IOEnv env ([b],[c],[d]) #-}
187 -- {-# SPECIALIZE zipWithM :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env [c] #-}
188 -- {-# SPECIALIZE zipWithM_ :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env () #-}
189 -- {-# SPECIALIZE anyM :: (a -> IOEnv env Bool) -> [a] -> IOEnv env Bool #-}
190 -- {-# SPECIALIZE when :: Bool -> IOEnv env a -> IOEnv env () #-}
191 -- {-# SPECIALIZE unless :: Bool -> IOEnv env a -> IOEnv env () #-}