I'd like to be able to use the UNPACK pragma on an existentially quantified
datatype. So as in the below example:
{-# LANGUAGE ExistentialQuantification #-}
data Foo = forall a. Show a => Foo !a
instance Show Foo where
show (Foo a) = "Foo! " ++ show a
data Bar =
Bar {-# UNPACK #-} !Foo
deriving (Show)
main :: IO ()
main = do
let foo = Foo "Hello"
bar = Bar foo
print bar
I would expect the `Foo` constructor to be unpacked into Bar, as if I had
written:
data Bar = forall a. Show a => Bar !a
However, instead I get the 'Ignoring unusable UNPACK pragma on the first
argument of ‘Bar’' warning. Is there a reason this shouldn't work, or a
workaround to get it to do so?
Cheers,
Nick
_______________________________________________
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
