Dimitry Golubovsky wrote:
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module Main where
import Data.Maybe
fun :: Show a => String -> Maybe a -> IO () fun s mb = do putStrLn s case mb of Nothing -> return () Just a -> do putStrLn (show a) return ()
main = fun "bla" Nothing
=============
compiles with Yhc and runs fine (even with only the first line of main, so there is no mentioning that a String is wrapped in Maybe).
This program shouldn't compile, it doesn't compile in either ghc or hugs and is definitely ambiguous. Looking at the core that Yhc generates: Main.main = let v234 = Prelude.Prelude.Show.Prelude.Integer in Main.fun v234 Main._LAMBDA243 Prelude.Nothing Main._LAMBDA243 = "bla" It's arbitrarily chosen to give the Show dictionary for 'Integer' (which is 'Prelude.Prelude.Show.Prelude.Integer'). Given that Yhc's type system is unmodified since nhc98 it's likely that this is a 'carry over' bug from nhc98. Thanks Tom