    module Data.Array.Repa.Eval.Target
            ( Target    (..)
            , fromList)
    where
    import Data.Array.Repa.Base
    import Data.Array.Repa.Shape
    import Control.Monad
    import System.IO.Unsafe

    -- Target ---------------------------------------------------------------------
    -- | Class of manifest array representations that can be constructed in parallel.
    class Target r e where

     -- | Mutable version of the representation.
     data MVec r e

     -- | Allocate a new mutable array of the given size.
     newMVec          :: Int -> IO (MVec r e)

     -- | Write an element into the mutable array.
     unsafeWriteMVec  :: MVec r e -> Int -> e -> IO ()

     -- | Freeze the mutable array into an immutable Repa array.
     unsafeFreezeMVec :: sh  -> MVec r e -> IO (Array r sh e)

     -- | Ensure the strucure of a mutable array is fully evaluated.
     deepSeqMVec      :: MVec r e -> a -> a

     -- | Ensure the array is still live at this point.
     --   Needed when the mutable array is a ForeignPtr with a finalizer.
     touchMVec        :: MVec r e -> IO ()

    -- | O(n). Construct a manifest array from a list.
    fromList :: (Shape sh, Target r e)
             => sh -> [e] -> Array r sh e
    fromList sh xx
     = unsafePerformIO
     $ do   let len = length xx
            if len /= size sh
             then error "Data.Array.Repa.Eval.Fill.fromList: provide array shape does not match list length"
             else do
                    mvec    <- newMVec len
                    zipWithM_ (unsafeWriteMVec mvec) [0..] xx
                    unsafeFreezeMVec sh mvec