2 -- The above warning supression flag is a temporary kludge.
3 -- While working on this module you are encouraged to remove it and fix
4 -- any warnings in the module. See
5 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
9 -- (c) The University of Glasgow 2002-2006
11 -- The IO Monad with an environment
15 IOEnv, -- Instance of Monad
17 -- Standard combinators, specialised
18 returnM, thenM, thenM_, failM, failWithM,
19 mappM, mappM_, mapSndM, sequenceM, sequenceM_,
21 mapAndUnzipM, mapAndUnzip3M,
22 checkM, ifM, zipWithM, zipWithM_,
24 -- Getting at the environment
25 getEnv, setEnv, updEnv,
27 runIOEnv, unsafeInterleaveM,
28 tryM, tryAllM, tryMostM, fixM,
31 IORef, newMutVar, readMutVar, writeMutVar, updMutVar
33 #include "HsVersions.h"
35 import Panic ( try, tryUser, tryMost, Exception(..) )
37 import Data.IORef ( IORef, newIORef, readIORef, writeIORef, modifyIORef )
38 import System.IO.Unsafe ( unsafeInterleaveIO )
39 import System.IO ( fixIO )
42 ----------------------------------------------------------------------
43 -- Defining the monad type
44 ----------------------------------------------------------------------
47 newtype IOEnv env a = IOEnv (env -> IO a)
50 instance Monad (IOEnv m) where
54 fail s = failM -- Ignore the string
56 instance Applicative (IOEnv m) where
58 IOEnv f <*> IOEnv x = IOEnv (\ env -> f env <*> x env )
60 instance Functor (IOEnv m) where
61 fmap f (IOEnv m) = IOEnv (\ env -> fmap f (m env))
63 returnM :: a -> IOEnv env a
64 returnM a = IOEnv (\ env -> return a)
66 thenM :: IOEnv env a -> (a -> IOEnv env b) -> IOEnv env b
67 thenM (IOEnv m) f = IOEnv (\ env -> do { r <- m env ;
70 thenM_ :: IOEnv env a -> IOEnv env b -> IOEnv env b
71 thenM_ (IOEnv m) f = IOEnv (\ env -> do { m env ; unIOEnv f env })
74 failM = IOEnv (\ env -> ioError (userError "IOEnv failure"))
76 failWithM :: String -> IOEnv env a
77 failWithM s = IOEnv (\ env -> ioError (userError s))
81 ----------------------------------------------------------------------
82 -- Fundmantal combinators specific to the monad
83 ----------------------------------------------------------------------
86 ---------------------------
87 runIOEnv :: env -> IOEnv env a -> IO a
88 runIOEnv env (IOEnv m) = m env
91 ---------------------------
93 -- Aargh! Not inlining fixTc alleviates a space leak problem.
94 -- Normally fixTc is used with a lazy tuple match: if the optimiser is
95 -- shown the definition of fixTc, it occasionally transforms the code
96 -- in such a way that the code generator doesn't spot the selector
99 fixM :: (a -> IOEnv env a) -> IOEnv env a
100 fixM f = IOEnv (\ env -> fixIO (\ r -> unIOEnv (f r) env))
103 ---------------------------
104 tryM :: IOEnv env r -> IOEnv env (Either Exception r)
105 -- Reflect UserError exceptions (only) into IOEnv monad
106 -- Other exceptions are not caught; they are simply propagated as exns
108 -- The idea is that errors in the program being compiled will give rise
109 -- to UserErrors. But, say, pattern-match failures in GHC itself should
110 -- not be caught here, else they'll be reported as errors in the program
112 tryM (IOEnv thing) = IOEnv (\ env -> tryUser (thing env))
114 tryAllM :: IOEnv env r -> IOEnv env (Either Exception r)
115 -- Catch *all* exceptions
116 -- This is used when running a Template-Haskell splice, when
117 -- even a pattern-match failure is a programmer error
118 tryAllM (IOEnv thing) = IOEnv (\ env -> try (thing env))
120 tryMostM :: IOEnv env r -> IOEnv env (Either Exception r)
121 tryMostM (IOEnv thing) = IOEnv (\ env -> tryMost (thing env))
123 ---------------------------
124 unsafeInterleaveM :: IOEnv env a -> IOEnv env a
125 unsafeInterleaveM (IOEnv m) = IOEnv (\ env -> unsafeInterleaveIO (m env))
128 ----------------------------------------------------------------------
129 -- Accessing input/output
130 ----------------------------------------------------------------------
132 instance MonadIO (IOEnv env) where
133 liftIO io = IOEnv (\ env -> io)
135 newMutVar :: a -> IOEnv env (IORef a)
136 newMutVar val = liftIO (newIORef val)
138 writeMutVar :: IORef a -> a -> IOEnv env ()
139 writeMutVar var val = liftIO (writeIORef var val)
141 readMutVar :: IORef a -> IOEnv env a
142 readMutVar var = liftIO (readIORef var)
144 updMutVar :: IORef a -> (a -> a) -> IOEnv env ()
145 updMutVar var upd = liftIO (modifyIORef var upd)
148 ----------------------------------------------------------------------
149 -- Accessing the environment
150 ----------------------------------------------------------------------
152 getEnv :: IOEnv env env
153 {-# INLINE getEnv #-}
154 getEnv = IOEnv (\ env -> return env)
156 setEnv :: env' -> IOEnv env' a -> IOEnv env a
157 {-# INLINE setEnv #-}
158 setEnv new_env (IOEnv m) = IOEnv (\ env -> m new_env)
160 updEnv :: (env -> env') -> IOEnv env' a -> IOEnv env a
161 {-# INLINE updEnv #-}
162 updEnv upd (IOEnv m) = IOEnv (\ env -> m (upd env))
165 ----------------------------------------------------------------------
166 -- Standard combinators, but specialised for this monad
168 ----------------------------------------------------------------------
170 mappM :: (a -> IOEnv env b) -> [a] -> IOEnv env [b]
171 mappM_ :: (a -> IOEnv env b) -> [a] -> IOEnv env ()
172 mapSndM :: (b -> IOEnv env c) -> [(a,b)] -> IOEnv env [(a,c)]
173 -- Funny names to avoid clash with Prelude
174 sequenceM :: [IOEnv env a] -> IOEnv env [a]
175 sequenceM_ :: [IOEnv env a] -> IOEnv env ()
176 foldlM :: (a -> b -> IOEnv env a) -> a -> [b] -> IOEnv env a
177 foldrM :: (b -> a -> IOEnv env a) -> a -> [b] -> IOEnv env a
178 mapAndUnzipM :: (a -> IOEnv env (b,c)) -> [a] -> IOEnv env ([b],[c])
179 mapAndUnzip3M :: (a -> IOEnv env (b,c,d)) -> [a] -> IOEnv env ([b],[c],[d])
180 checkM :: Bool -> IOEnv env a -> IOEnv env () -- Perform arg if bool is False
181 ifM :: Bool -> IOEnv env a -> IOEnv env () -- Perform arg if bool is True
182 anyM :: (a -> IOEnv env Bool) -> [a] -> IOEnv env Bool
184 mappM f [] = return []
185 mappM f (x:xs) = do { r <- f x; rs <- mappM f xs; return (r:rs) }
187 mapSndM f [] = return []
188 mapSndM f ((a,b):xs) = do { c <- f b; rs <- mapSndM f xs; return ((a,c):rs) }
190 mappM_ f [] = return ()
191 mappM_ f (x:xs) = f x >> mappM_ f xs
193 anyM f [] = return False
194 anyM f (x:xs) = do { b <- f x; if b then return True
197 zipWithM :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env [c]
198 zipWithM f [] bs = return []
199 zipWithM f as [] = return []
200 zipWithM f (a:as) (b:bs) = do { r <- f a b; rs <- zipWithM f as bs; return (r:rs) }
202 zipWithM_ :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env ()
203 zipWithM_ f [] bs = return ()
204 zipWithM_ f as [] = return ()
205 zipWithM_ f (a:as) (b:bs) = do { f a b; zipWithM_ f as bs }
207 sequenceM [] = return []
208 sequenceM (x:xs) = do { r <- x; rs <- sequenceM xs; return (r:rs) }
210 sequenceM_ [] = return ()
211 sequenceM_ (x:xs) = do { x; sequenceM_ xs }
213 foldlM k z [] = return z
214 foldlM k z (x:xs) = do { r <- k z x; foldlM k r xs }
216 foldrM k z [] = return z
217 foldrM k z (x:xs) = do { r <- foldrM k z xs; k x r }
219 mapAndUnzipM f [] = return ([],[])
220 mapAndUnzipM f (x:xs) = do { (r,s) <- f x;
221 (rs,ss) <- mapAndUnzipM f xs;
222 return (r:rs, s:ss) }
224 mapAndUnzip3M f [] = return ([],[], [])
225 mapAndUnzip3M f (x:xs) = do { (r,s,t) <- f x;
226 (rs,ss,ts) <- mapAndUnzip3M f xs;
227 return (r:rs, s:ss, t:ts) }
229 checkM True err = return ()
230 checkM False err = do { err; return () }
232 ifM True do_it = do { do_it; return () }
233 ifM False do_it = return ()