add System.Mem.Address to base

per libraries in progress discussion and https://phabricator.haskell.org/D5268

current state is this

{-# LANGUAGE MagicHash #-}

Module System.Mem.Address (
 -- * Types
  Addr(..),

  -- * Address arithmetic
  nullAddr, plusAddr, minusAddr, remAddr,

  -- * Conversion
  addrToInt, addrToPtr, ptrToAddr



  ) where



import GHC.Base ( Int(..) )
import GHC.Prim

import GHC.Exts (isTrue#)
import GHC.Ptr
import Foreign.Marshal.Utils

import Data.Typeable ( Typeable )
import Data.Data ( Data(..), mkNoRepType )


-- | A machine address
data Addr = Addr Addr# deriving ( Typeable )

instance Show Addr where
  showsPrec _ (Addr a) =
    showString "0x" . showHex (fromIntegral (I# (addr2Int# a)) :: Word)

instance Eq Addr where
  Addr a# == Addr b# = isTrue# (eqAddr# a# b#)
  Addr a# /= Addr b# = isTrue# (neAddr# a# b#)

instance Ord Addr where
  Addr a# > Addr b# = isTrue# (gtAddr# a# b#)
  Addr a# >= Addr b# = isTrue# (geAddr# a# b#)
  Addr a# < Addr b# = isTrue# (ltAddr# a# b#)
  Addr a# <= Addr b# = isTrue# (leAddr# a# b#)

instance Data Addr where
  toConstr _ = error "toConstr"
  gunfold _ _ = error "gunfold"
  dataTypeOf _ = mkNoRepType "Data.Primitive.Types.Addr"

-- | The null address
nullAddr :: Addr
nullAddr = Addr nullAddr#

infixl 6 `plusAddr`, `minusAddr`
infixl 7 `remAddr`

-- | Offset an address by the given number of bytes
plusAddr :: Addr -> Int -> Addr
plusAddr (Addr a#) (I# i#) = Addr (plusAddr# a# i#)

-- | Distance in bytes between two addresses. The result is only valid if the
-- difference fits in an 'Int'.
minusAddr :: Addr -> Addr -> Int
minusAddr (Addr a#) (Addr b#) = I# (minusAddr# a# b#)

-- | The remainder of the address and the integer.
remAddr :: Addr -> Int -> Int
remAddr (Addr a#) (I# i#) = I# (remAddr# a# i#)

-- | Convert an 'Addr' to an 'Int'.
addrToInt :: Addr -> Int
{-# INLINE addrToInt #-}
addrToInt (Addr addr#) = I# (addr2Int# addr#)

-- | convert `Addr` to `Ptr a`
addrToPtr :: Addr -> Ptr a
addrToPtr (Addr addr#) = Ptr addr#

-- | convert `Ptr a` to `Addr`
ptrToAddr :: Ptr a -> Addr
ptrToAddr (Ptr p) = Addr p

Trac metadata

Trac field	Value
Version	8.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions	D5268
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %8.8.1

changed weight to 5

added Tbug Trac import core libraries labels

Trac metadata

Trac field	Value
Type	Bug → FeatureRequest

added Tfeature request label and removed Tbug label

Fixed Phabricator link.

changed milestone to %8.10.1

carter, where is the discussion for this?

Regardless, this won't happen for 8.8.

the discussion started in https://mail.haskell.org/pipermail/libraries/2018-October/028997.html (https://mail.haskell.org/pipermail/libraries/2018-October/thread.html) and continued through november https://mail.haskell.org/pipermail/libraries/2018-November/thread.html

i'll write up more notes later, but ultimately the conclusion seems to be :

1. theres not really any examples where the code becomes simpler/safer/more performant with Address in base and usage thereof
2. there are valid/ real issues with some Ptr based interfaces and they could be improved. (and some confusion about why/best/practicies, and in one case the mistaken belief that all Ptr a values will conform to the Storable type class representation)

there were ~ 3 people arguing for inclusion in base, but in my own opinion there wasn't a case substantiating their utility. (and some of the exemplar changes they suggested would needless break existing code without fixing any underlying issue, as best i could tell)

Punchline: theres definitely a genuine need for better tooling around pointers to make its way into the ecosystem and perhaps eventually base, but this Adddress work doesn't accomplish that

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedWon'tFix

added Tbug label

added Pnormal label