On 2021-04-15 8:54 a.m., YueCompl via Haskell-Cafe wrote:
-- * Things not working managedArrayAsSeries::SomeManagedArray->IODynamic managedArrayAsSeries (SomeManagedArrayma)=do vec <-do SomeArraycap fp <-arrayAtTheMoment ma return $VS.unsafeFromForeignPtr0 fp cap letlen =return $VS.length vec rs i =return $vec VS.!i return $toDyn $Serieslen rs
That means you have this code fragment: arrayAtTheMoment ma
= \(SomeArray cap fp) -> return $ VS.unsafeFromForeignPtr0 fp cap
That means you have this function: \(SomeArray cap fp) -> return $ VS.unsafeFromForeignPtr0 fp cap Now you are violating the 1st restriction at https://downloads.haskell.org/ghc/latest/docs/html/users_guide/exts/existent... https://downloads.haskell.org/ghc/latest/docs/html/users_guide/exts/existent... There are two solutions. 1st solution: One more existential type. data Vec = forall a. (Typeable a, VS.Storable a) => Vec (VS.Vector a) Vec vec <- do SomeArray cap fp <- arrayAtTheMoment ma return (Vec (VS.unsafeFromForeignPtr0 fp cap)) 2nd solution: CPS transform. {-# language RankNTypes #-} {-# language BlockArguments #-} withSomeArray :: SomeArray -> (forall a. (Typeable a, VS.Storable a) => Int -> ForeignPtr a -> r) -> r withSomeArray (SomeArray i p) f = f i p sa <- arrayAtTheMoment ma withSomeArray sa \cap fp -> do let vec = VS.unsafeFromForeignPtr0 fp cap -- or if you prefer: vec <- return (VS.unsafeFromForeignPtr0 fp cap) len = return (VS.length vec) rs i = return (vec VS.! i) etc.