+\begin{code}
+{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
+{-# OPTIONS_HADDOCK hide #-}
+
-----------------------------------------------------------------------------
--- $Id: Ptr.lhs,v 1.3 2002/04/24 16:31:45 simonmar Exp $
---
--- (c) The FFI Task Force, 2000
-- |
--- Module GHC.Ptr
+-- Module : GHC.Ptr
+-- Copyright : (c) The FFI Task Force, 2000-2002
+-- License : see libraries/base/LICENSE
+--
+-- Maintainer : ffi@haskell.org
+-- Stability : internal
+-- Portability : non-portable (GHC Extensions)
+--
+-- The 'Ptr' and 'FunPtr' types and operations.
+--
+-----------------------------------------------------------------------------
-\begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+-- #hide
module GHC.Ptr where
import GHC.Base
+import GHC.Show
+import GHC.Num
+import GHC.List ( length, replicate )
+import Numeric ( showHex )
+
+#include "MachDeps.h"
------------------------------------------------------------------------
-- 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 often be an instance of class
+-- 'Foreign.Storable.Storable' which provides the marshalling operations.
+-- However this is not essential, and you can provide your own operations
+-- to access the pointer. For example you might write small foreign
+-- functions to get or set the fields of a C @struct@.
+
+-- |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 second to the first
+-- argument. We have
+--
+-- > p2 == p1 `plusPtr` (p2 `minusPtr` p1)
minusPtr :: Ptr a -> Ptr b -> Int
minusPtr (Ptr a1) (Ptr a2) = I# (minusAddr# a1 a2)
-instance CCallable (Ptr a)
-instance CReturnable (Ptr a)
-
------------------------------------------------------------------------
-- 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 function callable
+-- from foreign code. The type @a@ will normally be a /foreign type/,
+-- a function type with zero or more arguments where
+--
+-- * the argument types are /marshallable foreign types/,
+-- i.e. 'Char', 'Int', 'Double', 'Float',
+-- 'Bool', 'Data.Int.Int8', 'Data.Int.Int16', 'Data.Int.Int32',
+-- 'Data.Int.Int64', 'Data.Word.Word8', 'Data.Word.Word16',
+-- 'Data.Word.Word32', 'Data.Word.Word64', @'Ptr' a@, @'FunPtr' a@,
+-- @'Foreign.StablePtr.StablePtr' a@ or a renaming of any of these
+-- using @newtype@.
+--
+-- * the return type is either a marshallable foreign type or has the form
+-- @'IO' t@ where @t@ is a marshallable foreign type or @()@.
+--
+-- A value of type @'FunPtr' a@ may be a pointer to a foreign function,
+-- either returned by another foreign function or imported with a
+-- a static address import like
+--
+-- > foreign import ccall "stdlib.h &free"
+-- > p_free :: FunPtr (Ptr a -> IO ())
+--
+-- or a pointer to a Haskell function created using a /wrapper/ stub
+-- declared to produce a 'FunPtr' of the correct type. For example:
+--
+-- > type Compare = Int -> Int -> Bool
+-- > foreign import ccall "wrapper"
+-- > mkCompare :: Compare -> IO (FunPtr Compare)
+--
+-- Calls to wrapper stubs like @mkCompare@ allocate storage, which
+-- should be released with 'Foreign.Ptr.freeHaskellFunPtr' when no
+-- longer required.
+--
+-- To convert 'FunPtr' values to corresponding Haskell functions, one
+-- can define a /dynamic/ stub for the specific foreign type, e.g.
+--
+-- > type IntFunction = CInt -> IO ()
+-- > foreign import ccall "dynamic"
+-- > mkFun :: FunPtr IntFunction -> IntFunction
+
+-- |The constant 'nullFunPtr' contains a
+-- distinguished value of 'FunPtr' 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'.
+--
+-- /Note:/ this is valid only on architectures where data and function
+-- pointers range over the same set of addresses, and should only be used
+-- for bindings to external libraries whose interface already relies on
+-- this assumption.
castFunPtrToPtr :: FunPtr a -> Ptr b
castFunPtrToPtr (FunPtr addr) = Ptr addr
+-- |Casts a 'Ptr' to a 'FunPtr'.
+--
+-- /Note:/ this is valid only on architectures where data and function
+-- pointers range over the same set of addresses, and should only be used
+-- for bindings to external libraries whose interface already relies on
+-- this assumption.
castPtrToFunPtr :: Ptr a -> FunPtr b
castPtrToFunPtr (Ptr addr) = FunPtr addr
-instance CCallable (FunPtr a)
-instance CReturnable (FunPtr a)
+------------------------------------------------------------------------
+-- Show instances for Ptr and FunPtr
+
+instance Show (Ptr a) where
+ showsPrec _ (Ptr a) rs = pad_out (showHex (wordToInteger(int2Word#(addr2Int# a))) "")
+ where
+ -- want 0s prefixed to pad it out to a fixed length.
+ pad_out ls =
+ '0':'x':(replicate (2*SIZEOF_HSPTR - length ls) '0') ++ ls ++ rs
+
+instance Show (FunPtr a) where
+ showsPrec p = showsPrec p . castFunPtrToPtr
\end{code}
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