1 -- (c) The University of Glasgow 2002
3 -- The IO Monad with an environment
7 IOEnv, -- Instance of Monad
9 -- Standard combinators, specialised
10 returnM, thenM, thenM_, failM,
11 mappM, mappM_, mapSndM, sequenceM, sequenceM_,
13 mapAndUnzipM, mapAndUnzip3M,
14 checkM, ifM, zipWithM, zipWithM_,
16 -- Getting at the environment
17 getEnv, setEnv, updEnv,
19 runIOEnv, unsafeInterleaveM,
24 IORef, newMutVar, readMutVar, writeMutVar, updMutVar
26 #include "HsVersions.h"
28 import Panic ( tryJust )
29 import DATA_IOREF ( IORef, newIORef, readIORef, writeIORef )
30 import UNSAFE_IO ( unsafeInterleaveIO )
31 import FIX_IO ( fixIO )
32 import EXCEPTION ( Exception(..) )
33 import IO ( isUserError )
36 ----------------------------------------------------------------------
37 -- Defining the monad type
38 ----------------------------------------------------------------------
41 newtype IOEnv env a = IOEnv (env -> IO a)
44 instance Monad (IOEnv m) where
48 fail s = failM -- Ignore the string
50 returnM :: a -> IOEnv env a
51 returnM a = IOEnv (\ env -> return a)
53 thenM :: IOEnv env a -> (a -> IOEnv env b) -> IOEnv env b
54 thenM (IOEnv m) f = IOEnv (\ env -> do { r <- m env ;
57 thenM_ :: IOEnv env a -> IOEnv env b -> IOEnv env b
58 thenM_ (IOEnv m) f = IOEnv (\ env -> do { m env ; unIOEnv f env })
61 failM = IOEnv (\ env -> ioError (userError "IOEnv failure"))
65 ----------------------------------------------------------------------
66 -- Fundmantal combinators specific to the monad
67 ----------------------------------------------------------------------
70 ---------------------------
71 runIOEnv :: env -> IOEnv env a -> IO a
72 runIOEnv env (IOEnv m) = m env
75 ---------------------------
77 -- Aargh! Not inlining fixTc alleviates a space leak problem.
78 -- Normally fixTc is used with a lazy tuple match: if the optimiser is
79 -- shown the definition of fixTc, it occasionally transforms the code
80 -- in such a way that the code generator doesn't spot the selector
83 fixM :: (a -> IOEnv env a) -> IOEnv env a
84 fixM f = IOEnv (\ env -> fixIO (\ r -> unIOEnv (f r) env))
87 ---------------------------
88 tryM :: IOEnv env r -> IOEnv env (Either Exception r)
89 -- Reflect exception into IOEnv envonad
90 tryM (IOEnv thing) = IOEnv (\ env -> tryJust tc_errors (thing env))
92 #if __GLASGOW_HASKELL__ > 504 || __GLASGOW_HASKELL__ < 500
93 tc_errors e@(IOException ioe) | isUserError ioe = Just e
94 #elif __GLASGOW_HASKELL__ == 502
95 tc_errors e@(UserError _) = Just e
97 tc_errors e@(IOException ioe) | isUserError e = Just e
99 tc_errors _other = Nothing
100 -- type checker failures show up as UserErrors only
103 ---------------------------
104 unsafeInterleaveM :: IOEnv env a -> IOEnv env a
105 unsafeInterleaveM (IOEnv m) = IOEnv (\ env -> unsafeInterleaveIO (m env))
108 ----------------------------------------------------------------------
109 -- Accessing input/output
110 ----------------------------------------------------------------------
112 ioToIOEnv :: IO a -> IOEnv env a
113 ioToIOEnv io = IOEnv (\ env -> io)
115 newMutVar :: a -> IOEnv env (IORef a)
116 newMutVar val = IOEnv (\ env -> newIORef val)
118 writeMutVar :: IORef a -> a -> IOEnv env ()
119 writeMutVar var val = IOEnv (\ env -> writeIORef var val)
121 readMutVar :: IORef a -> IOEnv env a
122 readMutVar var = IOEnv (\ env -> readIORef var)
124 updMutVar :: IORef a -> (a->a) -> IOEnv env ()
125 updMutVar var upd_fn = IOEnv (\ env -> do { v <- readIORef var; writeIORef var (upd_fn v) })
128 ----------------------------------------------------------------------
129 -- Accessing the environment
130 ----------------------------------------------------------------------
132 getEnv :: IOEnv env env
133 {-# INLINE getEnv #-}
134 getEnv = IOEnv (\ env -> return env)
136 setEnv :: env' -> IOEnv env' a -> IOEnv env a
137 {-# INLINE setEnv #-}
138 setEnv new_env (IOEnv m) = IOEnv (\ env -> m new_env)
140 updEnv :: (env -> env') -> IOEnv env' a -> IOEnv env a
141 {-# INLINE updEnv #-}
142 updEnv upd (IOEnv m) = IOEnv (\ env -> m (upd env))
145 ----------------------------------------------------------------------
146 -- Standard combinators, but specialised for this monad
148 ----------------------------------------------------------------------
150 mappM :: (a -> IOEnv env b) -> [a] -> IOEnv env [b]
151 mappM_ :: (a -> IOEnv env b) -> [a] -> IOEnv env ()
152 mapSndM :: (b -> IOEnv env c) -> [(a,b)] -> IOEnv env [(a,c)]
153 -- Funny names to avoid clash with Prelude
154 sequenceM :: [IOEnv env a] -> IOEnv env [a]
155 sequenceM_ :: [IOEnv env a] -> IOEnv env ()
156 foldlM :: (a -> b -> IOEnv env a) -> a -> [b] -> IOEnv env a
157 mapAndUnzipM :: (a -> IOEnv env (b,c)) -> [a] -> IOEnv env ([b],[c])
158 mapAndUnzip3M :: (a -> IOEnv env (b,c,d)) -> [a] -> IOEnv env ([b],[c],[d])
159 checkM :: Bool -> IOEnv env () -> IOEnv env () -- Perform arg if bool is False
160 ifM :: Bool -> IOEnv env () -> IOEnv env () -- Perform arg if bool is True
162 mappM f [] = return []
163 mappM f (x:xs) = do { r <- f x; rs <- mappM f xs; return (r:rs) }
165 mapSndM f [] = return []
166 mapSndM f ((a,b):xs) = do { c <- f b; rs <- mapSndM f xs; return ((a,c):rs) }
168 mappM_ f [] = return ()
169 mappM_ f (x:xs) = f x >> mappM_ f xs
171 zipWithM :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env [c]
172 zipWithM f [] bs = return []
173 zipWithM f as [] = return []
174 zipWithM f (a:as) (b:bs) = do { r <- f a b; rs <- zipWithM f as bs; return (r:rs) }
176 zipWithM_ :: (a -> b -> IOEnv env c) -> [a] -> [b] -> IOEnv env ()
177 zipWithM_ f [] bs = return ()
178 zipWithM_ f as [] = return ()
179 zipWithM_ f (a:as) (b:bs) = do { f a b; zipWithM_ f as bs }
181 sequenceM [] = return []
182 sequenceM (x:xs) = do { r <- x; rs <- sequenceM xs; return (r:rs) }
184 sequenceM_ [] = return ()
185 sequenceM_ (x:xs) = do { x; sequenceM_ xs }
187 foldlM k z [] = return z
188 foldlM k z (x:xs) = do { r <- k z x; foldlM k r xs }
190 mapAndUnzipM f [] = return ([],[])
191 mapAndUnzipM f (x:xs) = do { (r,s) <- f x;
192 (rs,ss) <- mapAndUnzipM f xs;
193 return (r:rs, s:ss) }
195 mapAndUnzip3M f [] = return ([],[], [])
196 mapAndUnzip3M f (x:xs) = do { (r,s,t) <- f x;
197 (rs,ss,ts) <- mapAndUnzip3M f xs;
198 return (r:rs, s:ss, t:ts) }
200 checkM True err = return ()
201 checkM False err = err
203 ifM True do_it = do_it
204 ifM False do_it = return ()