X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FPtr.lhs;h=bf78f713bd04105f6264e53ce6b73af745431fc9;hb=41e8fba828acbae1751628af50849f5352b27873;hp=5c6191f0c941e215a6591bc49d911c79e5e9575e;hpb=b706340c451952adf230b5b8daecad8a1f34d714;p=ghc-base.git

diff --git a/GHC/Ptr.lhs b/GHC/Ptr.lhs
index 5c6191f..bf78f71 100644
--- a/GHC/Ptr.lhs
+++ b/GHC/Ptr.lhs
@@ -1,5 +1,7 @@
 \begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
+{-# OPTIONS_HADDOCK hide #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  GHC.Ptr
@@ -14,55 +16,145 @@
 --
 -----------------------------------------------------------------------------
 
+-- #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}