Unboxed Vectors of newtype'd values

[Simon Peyton-Jones]

I see the boring code, but I don't see what you *want*!  I'm guessing you want "generalised newtype deriving" but why does that not work?

S

| -----Original Message-----
| From: Bas van Dijk [mailto:v.dijk.bas at gmail.com]
| Sent: 04 June 2012 20:41
| To: Simon Peyton-Jones
| Cc: Johan Tibell; Bryan O'Sullivan; Jake McArthur; libraries at haskell.org
| Subject: Re: Unboxed Vectors of newtype'd values
| 
| On 4 June 2012 12:43, Simon Peyton-Jones <simonpj at microsoft.com> wrote:
| > | I'd like some compiler support for abstracting over unboxed values
| > | in general and e.g. generate Unbox instances automatically. Then we
| > | could have other unboxed structures than Vector.
| >
| > Could someone post an example or two of the problem being described
| here?
| 
| The following is some boring code I wrote a while back at work for
| storing UUIDs[1] in unboxed vectors:
| 
| {-# LANGUAGE MultiParamTypeClasses, TypeFamilies #-}
| 
| import Control.Monad (liftM)
| import Data.Word (Word32)
| 
| import Data.UUID (UUID)
| import qualified Data.UUID as UUID
| 
| import qualified Data.Vector.Unboxed         as VU
| import qualified Data.Vector.Generic         as VG
| import qualified Data.Vector.Generic.Mutable as VGM
| 
| newtype instance VU.MVector s UUID =
| 	MV_UUID (VU.MVector s (Word32, Word32, Word32, Word32))
| 
| newtype instance  VU.Vector UUID =
| 	V_UUID (VU.Vector (Word32, Word32, Word32, Word32))
| 
| instance VU.Unbox UUID
| 
| instance VGM.MVector VU.MVector UUID where
|   {-# INLINE basicLength #-}
|   {-# INLINE basicUnsafeSlice #-}
|   {-# INLINE basicOverlaps #-}
|   {-# INLINE basicUnsafeNew #-}
|   {-# INLINE basicUnsafeReplicate #-}
|   {-# INLINE basicUnsafeRead #-}
|   {-# INLINE basicUnsafeWrite #-}
|   {-# INLINE basicClear #-}
|   {-# INLINE basicSet #-}
|   {-# INLINE basicUnsafeCopy #-}
|   {-# INLINE basicUnsafeGrow #-}
|   basicLength (MV_UUID v) =
|     VGM.basicLength v
| 
|   basicUnsafeSlice i n (MV_UUID v) =
|     MV_UUID $ VGM.basicUnsafeSlice i n v
| 
|   basicOverlaps (MV_UUID v1) (MV_UUID v2) =
|     VGM.basicOverlaps v1 v2
| 
|   basicUnsafeNew n =
|     MV_UUID `liftM` VGM.basicUnsafeNew n
| 
|   basicUnsafeReplicate n uuid =
|     MV_UUID `liftM` VGM.basicUnsafeReplicate n (UUID.toWords uuid)
| 
|   basicUnsafeRead (MV_UUID v) i =
|     fromQuadruple `liftM` VGM.basicUnsafeRead v i
| 
|   basicUnsafeWrite (MV_UUID v) i uuid =
|     VGM.basicUnsafeWrite v i (UUID.toWords uuid)
| 
|   basicClear (MV_UUID v) =
|     VGM.basicClear v
| 
|   basicSet (MV_UUID v) uuid =
|     VGM.basicSet v (UUID.toWords uuid)
| 
|   basicUnsafeCopy (MV_UUID v1) (MV_UUID v2) =
|     VGM.basicUnsafeCopy v1 v2
| 
|   basicUnsafeMove (MV_UUID v1) (MV_UUID v2) =
|     VGM.basicUnsafeMove v1 v2
| 
|   basicUnsafeGrow (MV_UUID v) n =
|     MV_UUID `liftM` VGM.basicUnsafeGrow v n
| 
| instance VG.Vector VU.Vector UUID where
|   {-# INLINE basicUnsafeFreeze #-}
|   {-# INLINE basicUnsafeThaw #-}
|   {-# INLINE basicLength #-}
|   {-# INLINE basicUnsafeSlice #-}
|   {-# INLINE basicUnsafeIndexM #-}
|   {-# INLINE elemseq #-}
|   basicUnsafeFreeze (MV_UUID v) =
|     V_UUID `liftM` VG.basicUnsafeFreeze v
| 
|   basicUnsafeThaw (V_UUID v) =
|     MV_UUID `liftM` VG.basicUnsafeThaw v
| 
|   basicLength (V_UUID v) =
|     VG.basicLength v
| 
|   basicUnsafeSlice i n (V_UUID v) =
|     V_UUID $ VG.basicUnsafeSlice i n v
| 
|   basicUnsafeIndexM (V_UUID v) i =
|     fromQuadruple `liftM` VG.basicUnsafeIndexM v i
| 
|   basicUnsafeCopy (MV_UUID mv) (V_UUID v) =
|     VG.basicUnsafeCopy mv v
| 
|   elemseq _ uuid z = VG.elemseq (undefined :: VU.Vector a) a
|                    $ VG.elemseq (undefined :: VU.Vector a) b
|                    $ VG.elemseq (undefined :: VU.Vector a) c
|                    $ VG.elemseq (undefined :: VU.Vector a) d z
|       where
|         (a,b,c,d) = UUID.toWords uuid
| 
| fromQuadruple :: (Word32, Word32, Word32, Word32) -> UUID fromQuadruple
| (a,b,c,d) = UUID.fromWords a b c d
| 
| Regards,
| 
| Bas
| 
| [1]
| http://hackage.haskell.org/packages/archive/uuid/1.2.5/doc/html/Data-
| UUID.html