-#endif
-\end{code}
-
-Primitive marshaling
-
-Minimal complete definition: sizeOf, alignment, and one definition
-in each of the peek/poke families.
-
-\begin{code}
-{- |
-The member functions of this class facilitate writing values of
-primitive types to raw memory (which may have been allocated with the
-above mentioned routines) and reading values from blocks of raw
-memory. The class, furthermore, includes support for computing the
-storage requirements and alignment restrictions of storable types.
-
-Memory addresses are represented as values of type @'Ptr' a@, for some
-@a@ which is an instance of class 'Storable'. The type argument to
-'Ptr' helps provide some valuable type safety in FFI code (you can\'t
-mix pointers of different types without an explicit cast), while
-helping the Haskell type system figure out which marshalling method is
-needed for a given pointer.
-
-All marshalling between Haskell and a foreign language ultimately
-boils down to translating Haskell data structures into the binary
-representation of a corresponding data structure of the foreign
-language and vice versa. To code this marshalling in Haskell, it is
-necessary to manipulate primtive data types stored in unstructured
-memory blocks. The class 'Storable' facilitates this manipulation on
-all types for which it is instantiated, which are the standard basic
-types of Haskell, the fixed size @Int@ types ('Int8', 'Int16',
-'Int32', 'Int64'), the fixed size @Word@ types ('Word8', 'Word16',
-'Word32', 'Word64'), 'StablePtr', all types from "CTypes" and
-"CTypesISO", as well as 'Ptr'.
-
-Minimal complete definition: 'sizeOf', 'alignment', one of 'peek',
-'peekElemOff' and 'peekByteOff', and one of 'poke', 'pokeElemOff' and
-'pokeByteOff'.
--}
-
-class Storable a where
-
- sizeOf :: a -> Int
- -- ^ Computes the storage requirements (in bytes) of the argument.
- -- The value of the argument is not used.
-
- alignment :: a -> Int
- -- ^ Computes the alignment constraint of the argument. An
- -- alignment constraint @x@ is fulfilled by any address divisible
- -- by @x@. The value of the argument is not used.
-
- peekElemOff :: Ptr a -> Int -> IO a
- -- ^ Read a value from a memory area regarded as an array
- -- of values of the same kind. The first argument specifies
- -- the start address of the array and the second the index into
- -- the array (the first element of the array has index
- -- @0@). The following equality holds,
- --
- -- > peekElemOff addr idx = IOExts.fixIO $ \result ->
- -- > peek (addr \`plusPtr\` (idx * sizeOf result))
- --
- -- Note that this is only a specification, not
- -- necessarily the concrete implementation of the
- -- function.
-
- pokeElemOff :: Ptr a -> Int -> a -> IO ()
- -- ^ Write a value to a memory area regarded as an array of
- -- values of the same kind. The following equality holds:
- --
- -- > pokeElemOff addr idx x =
- -- > poke (addr \`plusPtr\` (idx * sizeOf x)) x
-
- peekByteOff :: Ptr b -> Int -> IO a
- -- ^ Read a value from a memory location given by a base
- -- address and offset. The following equality holds:
- --
- -- > peekByteOff addr off = peek (addr \`plusPtr\` off)
-
- pokeByteOff :: Ptr b -> Int -> a -> IO ()
- -- ^ Write a value to a memory location given by a base
- -- address and offset. The following equality holds:
- --
- -- > pokeByteOff addr off x = poke (addr \`plusPtr\` off) x
-
- peek :: Ptr a -> IO a
- -- ^ Read a value from the given memory location.
- --
- -- Note that the peek and poke functions might require properly
- -- aligned addresses to function correctly. This is architecture
- -- dependent; thus, portable code should ensure that when peeking or
- -- poking values of some type @a@, the alignment
- -- constraint for @a@, as given by the function
- -- 'alignment' is fulfilled.
-
- poke :: Ptr a -> a -> IO ()
- -- ^ Write the given value to the given memory location. Alignment
- -- restrictions might apply; see 'peek'.
-
- -- circular default instances
- peekElemOff = peekElemOff_ undefined
- where peekElemOff_ :: a -> Ptr a -> Int -> IO a
- peekElemOff_ undef ptr off = peekByteOff ptr (off * sizeOf undef)
- pokeElemOff ptr off val = pokeByteOff ptr (off * sizeOf val) val
-
- peekByteOff ptr off = peek (ptr `plusPtr` off)
- pokeByteOff ptr off = poke (ptr `plusPtr` off)
-
- peek ptr = peekElemOff ptr 0
- poke ptr = pokeElemOff ptr 0