[commit: ghc] master: Revert "Make Ptr's parameter phantom" (f251afe)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/f251afe4e450317c99defab9eeba63a0a998780b/ghc

>---------------------------------------------------------------

commit f251afe4e450317c99defab9eeba63a0a998780b
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Mon Jun 9 22:58:03 2014 +0200

    Revert "Make Ptr's parameter phantom"
    
    This reverts commit 1946922c61df427e59f8a00572fd4dd6501abd98, as it
    trips the build system over, and I don't see why.


>---------------------------------------------------------------

f251afe4e450317c99defab9eeba63a0a998780b
 libraries/base/Data/Coerce.hs |  3 ++-
 libraries/base/GHC/Ptr.lhs    | 10 ++--------
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/libraries/base/Data/Coerce.hs b/libraries/base/Data/Coerce.hs
index 9199835..fb38b36 100644
--- a/libraries/base/Data/Coerce.hs
+++ b/libraries/base/Data/Coerce.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE Unsafe #-}
-{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE AutoDeriveTypeable #-}
+{-# LANGUAGE StandaloneDeriving #-}
 
 -----------------------------------------------------------------------------
 -- |
diff --git a/libraries/base/GHC/Ptr.lhs b/libraries/base/GHC/Ptr.lhs
index 341512b..c959d1e 100644
--- a/libraries/base/GHC/Ptr.lhs
+++ b/libraries/base/GHC/Ptr.lhs
@@ -31,13 +31,13 @@ import GHC.Show
 import GHC.Num
 import GHC.List ( length, replicate )
 import Numeric          ( showHex )
-import Data.Coerce
 
 #include "MachDeps.h"
 
 ------------------------------------------------------------------------
 -- Data pointers.
 
+type role Ptr representational
 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
@@ -49,10 +49,6 @@ data Ptr a = Ptr Addr# deriving (Eq, Ord)
 -- to access the pointer.  For example you might write small foreign
 -- functions to get or set the fields of a C @struct at .
 
--- The role of Ptr's parameter is phantom, as there is relation between
--- the Haskell representation and whathever the user puts at the end of the
--- pointer. And phantom is useful to implement castPtr (see #9163)
-
 -- |The constant 'nullPtr' contains a distinguished value of 'Ptr'
 -- that is not associated with a valid memory location.
 nullPtr :: Ptr a
@@ -60,7 +56,7 @@ nullPtr = Ptr nullAddr#
 
 -- |The 'castPtr' function casts a pointer from one type to another.
 castPtr :: Ptr a -> Ptr b
-castPtr = coerce
+castPtr (Ptr addr) = Ptr addr
 
 -- |Advances the given address by the given offset in bytes.
 plusPtr :: Ptr a -> Int -> Ptr b
@@ -128,8 +124,6 @@ data FunPtr a = FunPtr Addr# deriving (Eq, Ord)
 -- > foreign import ccall "dynamic" 
 -- >   mkFun :: FunPtr IntFunction -> IntFunction
 
--- The role of FunPtr is representational, to be on the safe side (see #9163)
-
 -- |The constant 'nullFunPtr' contains a
 -- distinguished value of 'FunPtr' that is not
 -- associated with a valid memory location.