[Haskell-cafe] CBN, CBV, Lazy in the same final tagless framework

[Felipe Lessa]

On Thu, Oct 08, 2009 at 12:54:14AM -0700, oleg at 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)

Thanks,

--
Felipe.