[Yhc] instance Monad IO bug

[Bernie Pope]

> for a file
> main = print "hi" >> return undefined >> print "bye"
> ghc, hugs and nhc98 print
> "hi"
> "bye"
> yhc prints
> "hi"
> Prelude.undefined


That is strange.

In my version of Yhc it works as expected (same as Hugs and
GHC).

The instance of IO for Monad in my version is:

\begin{code}
instance Monad IO where
    x >>= y  = IO (primBind1 x y)
           where
        primBind1 (IO xf) y w =
          case xf w of
            Right xv -> case y xv of
                                  IO yv -> yv w
            Left err -> Left err -- Changing type
    x >>  y  = IO (primBind2 x y)
           where
        primBind2 (IO xf) y w =
          case xf w of
            Right xv -> case y of
                                  IO yv -> yv w
            Left err -> Left err -- Changing type
    return a = IO (primReturn a)
               where
                 primReturn a w = Right a
\end{code}

To my eyes there is no strictness problem in this
definition.

Also, in my version IO is defined this way:

\begin{code}
data World = World
newtype IO a = IO (World -> Either IOError a)
\end{code}

>From memory this is the same as it was in nhc98.

I haven't done a darcs pull for a week or so; perhaps my
version is older than yours?

Cheers,
Bernie.