On 02/04/2010, at 13:01, Don Stewart wrote:
rl:
replicate :: Int -> a -> New a replicate n x = Generic.New.unstream (Fusion.Stream.replicate n x)
and then either
Mutable.run (replicate n x)
to get a mutable vector or
new (replicate n x)
Hmm, but here 'a' is pure. I don't think he wants
newWith :: (PrimMonad m, MVector v a) => Int -> a -> m (v (PrimState m) a)
but more:
newWithM :: (PrimMonad m, MVector v a) => Int -> m a -> m (v (PrimState m) a)
Ah. I missed that. Then your best bet is probably replicate n action = munstream v $ Fusion.Stream.Monadic.generateM n (const action) $ new n It's uglier that it should be but vector simply doesn't define the right combinators for this at the moment.
to get an immutable one. You could also chain operations on New, including monadic ones:
v <- Mutable.run $ Generic.New.transform (Fusion.Stream.Monadic.mapM f) $ replicate n x
Oh, that's interesting. But what if we want to fill directly with the monadic action? We wouldn't
mapM (const a) $ replicate n undefined
So how do we best do a fusible, e.g.:
replicateM :: G.Vector v a => Int -> IO a -> IO (v a)
There are two things one would have to do. First, add a function to Generic.New which initialises a New from a Monadic.Stream and fusion rules for it. That's easy. The hard part is to generalise New to work with arbitrary monads: at the moment it is defined as: data New a = New (forall mv s. MVector mv a => ST s (mv s a)) This is because its basic reason for existence is to be passed to Vector.new which then does a runST to produce an immutable vector. It is perhaps possible to make New more general but it's quite tricky. I'll think about it after the ICFP deadline :-) Roman