1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
4 -- Module : Foreign.Storable
5 -- Copyright : (c) The FFI task force 2001
6 -- License : see libraries/base/LICENSE
8 -- Maintainer : ffi@haskell.org
9 -- Stability : provisional
10 -- Portability : portable
12 -- The module "Foreign.Storable" provides most elementary support for
13 -- marshalling and is part of the language-independent portion of the
14 -- Foreign Function Interface (FFI), and will normally be imported via
15 -- the "Foreign" module.
17 -----------------------------------------------------------------------------
19 module Foreign.Storable
21 sizeOf, -- :: a -> Int
22 alignment, -- :: a -> Int
23 peekElemOff, -- :: Ptr a -> Int -> IO a
24 pokeElemOff, -- :: Ptr a -> Int -> a -> IO ()
25 peekByteOff, -- :: Ptr b -> Int -> IO a
26 pokeByteOff, -- :: Ptr b -> Int -> a -> IO ()
27 peek, -- :: Ptr a -> IO a
28 poke) -- :: Ptr a -> a -> IO ()
33 import NHC.FFI (Storable(..),Ptr,FunPtr,StablePtr
34 ,Int8,Int16,Int32,Int64,Word8,Word16,Word32,Word64)
37 import Control.Monad ( liftM )
42 #ifdef __GLASGOW_HASKELL__
44 import GHC.Stable ( StablePtr )
58 import Foreign.StablePtr
67 The member functions of this class facilitate writing values of
68 primitive types to raw memory (which may have been allocated with the
69 above mentioned routines) and reading values from blocks of raw
70 memory. The class, furthermore, includes support for computing the
71 storage requirements and alignment restrictions of storable types.
73 Memory addresses are represented as values of type @'Ptr' a@, for some
74 @a@ which is an instance of class 'Storable'. The type argument to
75 'Ptr' helps provide some valuable type safety in FFI code (you can\'t
76 mix pointers of different types without an explicit cast), while
77 helping the Haskell type system figure out which marshalling method is
78 needed for a given pointer.
80 All marshalling between Haskell and a foreign language ultimately
81 boils down to translating Haskell data structures into the binary
82 representation of a corresponding data structure of the foreign
83 language and vice versa. To code this marshalling in Haskell, it is
84 necessary to manipulate primtive data types stored in unstructured
85 memory blocks. The class 'Storable' facilitates this manipulation on
86 all types for which it is instantiated, which are the standard basic
87 types of Haskell, the fixed size @Int@ types ('Int8', 'Int16',
88 'Int32', 'Int64'), the fixed size @Word@ types ('Word8', 'Word16',
89 'Word32', 'Word64'), 'StablePtr', all types from "Foreign.C.Types",
92 Minimal complete definition: 'sizeOf', 'alignment', one of 'peek',
93 'peekElemOff' and 'peekByteOff', and one of 'poke', 'pokeElemOff' and
97 class Storable a where
100 -- ^ Computes the storage requirements (in bytes) of the argument.
101 -- The value of the argument is not used.
103 alignment :: a -> Int
104 -- ^ Computes the alignment constraint of the argument. An
105 -- alignment constraint @x@ is fulfilled by any address divisible
106 -- by @x@. The value of the argument is not used.
108 peekElemOff :: Ptr a -> Int -> IO a
109 -- ^ Read a value from a memory area regarded as an array
110 -- of values of the same kind. The first argument specifies
111 -- the start address of the array and the second the index into
112 -- the array (the first element of the array has index
113 -- @0@). The following equality holds,
115 -- > peekElemOff addr idx = IOExts.fixIO $ \result ->
116 -- > peek (addr \`plusPtr\` (idx * sizeOf result))
118 -- Note that this is only a specification, not
119 -- necessarily the concrete implementation of the
122 pokeElemOff :: Ptr a -> Int -> a -> IO ()
123 -- ^ Write a value to a memory area regarded as an array of
124 -- values of the same kind. The following equality holds:
126 -- > pokeElemOff addr idx x =
127 -- > poke (addr \`plusPtr\` (idx * sizeOf x)) x
129 peekByteOff :: Ptr b -> Int -> IO a
130 -- ^ Read a value from a memory location given by a base
131 -- address and offset. The following equality holds:
133 -- > peekByteOff addr off = peek (addr \`plusPtr\` off)
135 pokeByteOff :: Ptr b -> Int -> a -> IO ()
136 -- ^ Write a value to a memory location given by a base
137 -- address and offset. The following equality holds:
139 -- > pokeByteOff addr off x = poke (addr \`plusPtr\` off) x
141 peek :: Ptr a -> IO a
142 -- ^ Read a value from the given memory location.
144 -- Note that the peek and poke functions might require properly
145 -- aligned addresses to function correctly. This is architecture
146 -- dependent; thus, portable code should ensure that when peeking or
147 -- poking values of some type @a@, the alignment
148 -- constraint for @a@, as given by the function
149 -- 'alignment' is fulfilled.
151 poke :: Ptr a -> a -> IO ()
152 -- ^ Write the given value to the given memory location. Alignment
153 -- restrictions might apply; see 'peek'.
155 -- circular default instances
156 #ifdef __GLASGOW_HASKELL__
157 peekElemOff = peekElemOff_ undefined
158 where peekElemOff_ :: a -> Ptr a -> Int -> IO a
159 peekElemOff_ undef ptr off = peekByteOff ptr (off * sizeOf undef)
161 peekElemOff ptr off = peekByteOff ptr (off * sizeOfPtr ptr undefined)
163 pokeElemOff ptr off val = pokeByteOff ptr (off * sizeOf val) val
165 peekByteOff ptr off = peek (ptr `plusPtr` off)
166 pokeByteOff ptr off = poke (ptr `plusPtr` off)
168 peek ptr = peekElemOff ptr 0
169 poke ptr = pokeElemOff ptr 0
171 #ifndef __GLASGOW_HASKELL__
172 sizeOfPtr :: Storable a => Ptr a -> a -> Int
173 sizeOfPtr px x = sizeOf x
176 -- System-dependent, but rather obvious instances
178 instance Storable Bool where
179 sizeOf _ = sizeOf (undefined::HTYPE_INT)
180 alignment _ = alignment (undefined::HTYPE_INT)
181 peekElemOff p i = liftM (/= (0::HTYPE_INT)) $ peekElemOff (castPtr p) i
182 pokeElemOff p i x = pokeElemOff (castPtr p) i (if x then 1 else 0::HTYPE_INT)
184 #define STORABLE(T,size,align,read,write) \
185 instance Storable (T) where { \
187 alignment _ = align; \
188 peekElemOff = read; \
189 pokeElemOff = write }
191 #ifdef __GLASGOW_HASKELL__
192 STORABLE(Char,SIZEOF_INT32,ALIGNMENT_INT32,
193 readWideCharOffPtr,writeWideCharOffPtr)
194 #elif defined(__HUGS__)
195 STORABLE(Char,SIZEOF_CHAR,ALIGNMENT_HSCHAR,
196 readCharOffPtr,writeCharOffPtr)
199 STORABLE(Int,SIZEOF_HSINT,ALIGNMENT_HSINT,
200 readIntOffPtr,writeIntOffPtr)
202 #ifdef __GLASGOW_HASKELL__
203 STORABLE(Word,SIZEOF_HSWORD,ALIGNMENT_HSWORD,
204 readWordOffPtr,writeWordOffPtr)
207 STORABLE((Ptr a),SIZEOF_HSPTR,ALIGNMENT_HSPTR,
208 readPtrOffPtr,writePtrOffPtr)
210 STORABLE((FunPtr a),SIZEOF_HSFUNPTR,ALIGNMENT_HSFUNPTR,
211 readFunPtrOffPtr,writeFunPtrOffPtr)
213 STORABLE((StablePtr a),SIZEOF_HSSTABLEPTR,ALIGNMENT_HSSTABLEPTR,
214 readStablePtrOffPtr,writeStablePtrOffPtr)
216 STORABLE(Float,SIZEOF_HSFLOAT,ALIGNMENT_HSFLOAT,
217 readFloatOffPtr,writeFloatOffPtr)
219 STORABLE(Double,SIZEOF_HSDOUBLE,ALIGNMENT_HSDOUBLE,
220 readDoubleOffPtr,writeDoubleOffPtr)
222 STORABLE(Word8,SIZEOF_WORD8,ALIGNMENT_WORD8,
223 readWord8OffPtr,writeWord8OffPtr)
225 STORABLE(Word16,SIZEOF_WORD16,ALIGNMENT_WORD16,
226 readWord16OffPtr,writeWord16OffPtr)
228 STORABLE(Word32,SIZEOF_WORD32,ALIGNMENT_WORD32,
229 readWord32OffPtr,writeWord32OffPtr)
231 STORABLE(Word64,SIZEOF_WORD64,ALIGNMENT_WORD64,
232 readWord64OffPtr,writeWord64OffPtr)
234 STORABLE(Int8,SIZEOF_INT8,ALIGNMENT_INT8,
235 readInt8OffPtr,writeInt8OffPtr)
237 STORABLE(Int16,SIZEOF_INT16,ALIGNMENT_INT16,
238 readInt16OffPtr,writeInt16OffPtr)
240 STORABLE(Int32,SIZEOF_INT32,ALIGNMENT_INT32,
241 readInt32OffPtr,writeInt32OffPtr)
243 STORABLE(Int64,SIZEOF_INT64,ALIGNMENT_INT64,
244 readInt64OffPtr,writeInt64OffPtr)