On Fri, Oct 9, 2009 at 11:12 AM, Felipe Lessa <felipe.le...@gmail.com> wrote:
> On Thu, Oct 08, 2009 at 12:54:14AM -0700, o...@okmij.org wrote:
>> Actually it is possible to implement all three evaluation orders
>> within the same final tagless framework, using the same interpretation
>> of types and reusing most of the code save the semantics of lam. That
>> is where the three orders differ, by their own definition.
>
> That's really nice, Oleg, thanks! I just wanted to comment that
> I'd prefer to write
>
> share :: IO a -> IO (IO a)
> share m = mdo r <- newIORef (do x <- m
> writeIORef r (return x)
> return x)
> return (readIORef r >>= id)
>
> which unfortunately needs {-# LANGUAGE RecursiveDo #-} or
> some ugliness from mfix
>
> share :: IO a -> IO (IO a)
> share m = do r <- mfix $ \r -> newIORef (do x <- m
> writeIORef r (return x)
> return x)
> return (readIORef r >>= id)
>
Alternatively,
share m = do
r <- newIORef undefined
writeIORef r $ do
x <- m
writeIORef r (return x)
return x
return $ readIORef r >>= id
Which is basically the same as your version, but only needs one IORef.
--
Dave Menendez <d...@zednenem.com>
<http://www.eyrie.org/~zednenem/>
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