-- Data pointers.
data Ptr a = Ptr Addr# deriving (Eq, Ord)
+-- ^ A value of type @'Ptr' a@ represents a pointer to an object, or an
+-- array of objects, which may be marshalled to or from Haskell values
+-- of type @a@.
+--
+-- The type @a@ will normally be an instance of class
+-- 'Foreign.Storable.Storable' which provides the marshalling operations.
+
+-- |The constant 'nullPtr' contains a distinguished value of 'Ptr'
+-- that is not associated with a valid memory location.
nullPtr :: Ptr a
nullPtr = Ptr nullAddr#
+-- |The 'castPtr' function casts a pointer from one type to another.
castPtr :: Ptr a -> Ptr b
castPtr (Ptr addr) = Ptr addr
+-- |Advances the given address by the given offset in bytes.
plusPtr :: Ptr a -> Int -> Ptr b
plusPtr (Ptr addr) (I# d) = Ptr (plusAddr# addr d)
+-- |Given an arbitrary address and an alignment constraint,
+-- 'alignPtr' yields the next higher address that fulfills the
+-- alignment constraint. An alignment constraint @x@ is fulfilled by
+-- any address divisible by @x@. This operation is idempotent.
alignPtr :: Ptr a -> Int -> Ptr a
alignPtr addr@(Ptr a) (I# i)
= case remAddr# a i of {
0# -> addr;
n -> Ptr (plusAddr# a (i -# n)) }
+-- |Computes the offset required to get from the first to the second
+-- argument. We have
+--
+-- > p2 == p1 \`'plusPtr'\` (p2 \`'minusPtr'\` p1)
minusPtr :: Ptr a -> Ptr b -> Int
minusPtr (Ptr a1) (Ptr a2) = I# (minusAddr# a1 a2)
-- Function pointers for the default calling convention.
data FunPtr a = FunPtr Addr# deriving (Eq, Ord)
+-- ^ A value of type @'FunPtr' a@ is a pointer to a piece of code. It
+-- may be the pointer to a C function or to a Haskell function created
+-- using @foreign export dynamic@. A @foreign export
+-- dynamic@ should normally be declared to produce a
+-- 'FunPtr' of the correct type. For example:
+--
+-- > type Compare = 'Int' -> 'Int' -> 'Bool'
+-- > foreign export dynamic mkCompare :: Compare -> 'IO' ('FunPtr' Compare)
+-- |The constant 'nullFunPtr' contains a
+-- distinguished value of 'Ptr' that is not
+-- associated with a valid memory location
nullFunPtr :: FunPtr a
nullFunPtr = FunPtr nullAddr#
+-- |Casts a 'FunPtr' to a 'FunPtr' of a different type
castFunPtr :: FunPtr a -> FunPtr b
castFunPtr (FunPtr addr) = FunPtr addr
+-- |Casts a 'FunPtr' to a 'Ptr'
castFunPtrToPtr :: FunPtr a -> Ptr b
castFunPtrToPtr (FunPtr addr) = Ptr addr
+-- |Casts a 'Ptr' to a 'FunPtr'
castPtrToFunPtr :: Ptr a -> FunPtr b
castPtrToFunPtr (Ptr addr) = FunPtr addr