[project @ 2005-01-11 16:04:08 by simonmar]
[packages/old-time.git] / Foreign / Marshal / Utils.hs
1 {-# OPTIONS_GHC -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
3 -- |
4 -- Module : Foreign.Marshal.Utils
5 -- Copyright : (c) The FFI task force 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
7 --
8 -- Maintainer : ffi@haskell.org
9 -- Stability : provisional
10 -- Portability : portable
11 --
12 -- Utilities for primitive marshaling
13 --
14 -----------------------------------------------------------------------------
15
16 module Foreign.Marshal.Utils (
17 -- * General marshalling utilities
18
19 -- ** Combined allocation and marshalling
20 --
21 with, -- :: Storable a => a -> (Ptr a -> IO b) -> IO b
22 new, -- :: Storable a => a -> IO (Ptr a)
23
24 -- ** Marshalling of Boolean values (non-zero corresponds to 'True')
25 --
26 fromBool, -- :: Num a => Bool -> a
27 toBool, -- :: Num a => a -> Bool
28
29 -- ** Marshalling of Maybe values
30 --
31 maybeNew, -- :: ( a -> IO (Ptr a))
32 -- -> (Maybe a -> IO (Ptr a))
33 maybeWith, -- :: ( a -> (Ptr b -> IO c) -> IO c)
34 -- -> (Maybe a -> (Ptr b -> IO c) -> IO c)
35 maybePeek, -- :: (Ptr a -> IO b )
36 -- -> (Ptr a -> IO (Maybe b))
37
38 -- ** Marshalling lists of storable objects
39 --
40 withMany, -- :: (a -> (b -> res) -> res) -> [a] -> ([b] -> res) -> res
41
42 -- ** Haskellish interface to memcpy and memmove
43 -- | (argument order: destination, source)
44 --
45 copyBytes, -- :: Ptr a -> Ptr a -> Int -> IO ()
46 moveBytes, -- :: Ptr a -> Ptr a -> Int -> IO ()
47
48 -- ** DEPRECATED FUNCTIONS (don\'t use; they may disappear at any time)
49 --
50 withObject -- :: Storable a => a -> (Ptr a -> IO b) -> IO b
51 ) where
52
53 import Data.Maybe
54 import Foreign.Ptr ( Ptr, nullPtr )
55 import Foreign.Storable ( Storable(poke) )
56 import Foreign.C.Types ( CSize )
57 import Foreign.Marshal.Alloc ( malloc, alloca )
58
59 #ifdef __GLASGOW_HASKELL__
60 import GHC.IOBase
61 import GHC.Real ( fromIntegral )
62 import GHC.Num
63 import GHC.Base
64 #endif
65
66 #ifdef __NHC__
67 import Foreign.C.Types ( CInt(..) )
68 #endif
69
70 -- combined allocation and marshalling
71 -- -----------------------------------
72
73 -- |Allocate a block of memory and marshal a value into it
74 -- (the combination of 'malloc' and 'poke').
75 -- The size of the area allocated is determined by the 'Foreign.Storable.sizeOf'
76 -- method from the instance of 'Storable' for the appropriate type.
77 --
78 -- The memory may be deallocated using 'Foreign.Marshal.Alloc.free' or
79 -- 'Foreign.Marshal.Alloc.finalizerFree' when no longer required.
80 --
81 new :: Storable a => a -> IO (Ptr a)
82 new val =
83 do
84 ptr <- malloc
85 poke ptr val
86 return ptr
87
88 -- |@'with' val f@ executes the computation @f@, passing as argument
89 -- a pointer to a temporarily allocated block of memory into which
90 -- 'val' has been marshalled (the combination of 'alloca' and 'poke').
91 --
92 -- The memory is freed when @f@ terminates (either normally or via an
93 -- exception), so the pointer passed to @f@ must /not/ be used after this.
94 --
95 with :: Storable a => a -> (Ptr a -> IO b) -> IO b
96 with val f =
97 alloca $ \ptr -> do
98 poke ptr val
99 res <- f ptr
100 return res
101
102 -- old DEPRECATED name (don't use; may disappear at any time)
103 --
104 withObject :: Storable a => a -> (Ptr a -> IO b) -> IO b
105 {-# DEPRECATED withObject "use `with' instead" #-}
106 withObject = with
107
108
109 -- marshalling of Boolean values (non-zero corresponds to 'True')
110 -- -----------------------------
111
112 -- |Convert a Haskell 'Bool' to its numeric representation
113 --
114 fromBool :: Num a => Bool -> a
115 fromBool False = 0
116 fromBool True = 1
117
118 -- |Convert a Boolean in numeric representation to a Haskell value
119 --
120 toBool :: Num a => a -> Bool
121 toBool = (/= 0)
122
123
124 -- marshalling of Maybe values
125 -- ---------------------------
126
127 -- |Allocate storage and marshall a storable value wrapped into a 'Maybe'
128 --
129 -- * the 'nullPtr' is used to represent 'Nothing'
130 --
131 maybeNew :: ( a -> IO (Ptr a))
132 -> (Maybe a -> IO (Ptr a))
133 maybeNew = maybe (return nullPtr)
134
135 -- |Converts a @withXXX@ combinator into one marshalling a value wrapped
136 -- into a 'Maybe', using 'nullPtr' to represent 'Nothing'.
137 --
138 maybeWith :: ( a -> (Ptr b -> IO c) -> IO c)
139 -> (Maybe a -> (Ptr b -> IO c) -> IO c)
140 maybeWith = maybe ($ nullPtr)
141
142 -- |Convert a peek combinator into a one returning 'Nothing' if applied to a
143 -- 'nullPtr'
144 --
145 maybePeek :: (Ptr a -> IO b) -> Ptr a -> IO (Maybe b)
146 maybePeek peek ptr | ptr == nullPtr = return Nothing
147 | otherwise = do a <- peek ptr; return (Just a)
148
149
150 -- marshalling lists of storable objects
151 -- -------------------------------------
152
153 -- |Replicates a @withXXX@ combinator over a list of objects, yielding a list of
154 -- marshalled objects
155 --
156 withMany :: (a -> (b -> res) -> res) -- withXXX combinator for one object
157 -> [a] -- storable objects
158 -> ([b] -> res) -- action on list of marshalled obj.s
159 -> res
160 withMany _ [] f = f []
161 withMany withFoo (x:xs) f = withFoo x $ \x' ->
162 withMany withFoo xs (\xs' -> f (x':xs'))
163
164
165 -- Haskellish interface to memcpy and memmove
166 -- ------------------------------------------
167
168 -- |Copies the given number of bytes from the second area (source) into the
169 -- first (destination); the copied areas may /not/ overlap
170 --
171 copyBytes :: Ptr a -> Ptr a -> Int -> IO ()
172 copyBytes dest src size = memcpy dest src (fromIntegral size)
173
174 -- |Copies the given number of elements from the second area (source) into the
175 -- first (destination); the copied areas /may/ overlap
176 --
177 moveBytes :: Ptr a -> Ptr a -> Int -> IO ()
178 moveBytes dest src size = memmove dest src (fromIntegral size)
179
180
181 -- auxilliary routines
182 -- -------------------
183
184 -- |Basic C routines needed for memory copying
185 --
186 foreign import ccall unsafe "string.h" memcpy :: Ptr a -> Ptr a -> CSize -> IO ()
187 foreign import ccall unsafe "string.h" memmove :: Ptr a -> Ptr a -> CSize -> IO ()