I'm currently working with a lot of very short arrays of fixed length and as a thought experiment I thought I would try to play with fast numeric field accessors In particular, I'd like to use something like foreign prim to do something like
foreign import prim "cmm_getField" unsafeField# :: a -> Int# -> b
unsafeField :: a -> Int -> b unsafeField a (I# i) = a' `pseq` unsafeField# a' i -- the pseq could be moved into the prim, I suppose. where a' = unsafeCoerce a
fst :: (a,b) -> a fst = unsafeField 0
snd :: (a,b) -> b snd = unsafeField 1
This becomes more reasonable to consider when you are forced to make something like
data V4 a = V4 a a a a
using
unsafeIndex (V4 a _ _ _) 0 = a unsafeIndex (V4 _ b _ _) 1 = b unsafeIndex (V4 _ _ c _) 2 = c unsafeIndex (V4 _ _ _ d) 3 = d
rather than
unsafeIndex :: V4 a -> Int -> a unsafeIndex = unsafeField
But I can only pass unboxed types to foreign prim. Is this an intrinsic limitation or just an artifact of the use cases that have presented themselves to date?