On Sat, Mar 19, 2005 at 12:17:46PM -0700, Kevin Atkinson wrote:
On Sat, 19 Mar 2005 ross@soi.city.ac.uk wrote:
I would also have expected loopFG to have been defined using fixIO.
Could you be more specific. Ie How?
For the type definitions newtype FG' a b = FG' (Control -> a -> IO (Control, b)) newtype FG a b = FG (FGState -> IO (FG' a b, FGState)) newtype Container a b = Container (FG ([WidgetP], a) b) the usual instances would be (give or take a ~): instance Arrow FG' where arr f = FG' $ \ c x -> return (c, f x) FG' f >>> FG' g = FG' $ \ c x -> do (c', x') <- f c x g c' x' first (FG' f) = FG' $ \ c (x, y) -> do (c', x') <- f c x return (c', (x', y)) instance ArrowLoop FG' where loop (FG' f) = FG' $ \ c x -> do (c', x', _) <- mfix $ \ ~(_, _, y) -> do ~(c', ~(x', y')) <- f c (x, y) return (c', x', y') return (c', x') instance Arrow FG where arr f = FG $ \ s -> return (arr f, s) FG f >>> FG g = FG $ \ s -> do (f', s') <- f s (g', s'') <- g s return (f' >>> g', s'') first (FG f) = FG $ \ s -> do (f', s') <- f s return (first f', s') instance ArrowLoop FG where loop (FG f) = FG $ \ s -> do (f', s') <- f s return (loop f', s') instance Arrow Container where arr f = Container (arr (f . snd)) Container f >>> Container g = Container $ arr (\ (ws, a) -> (ws, (ws, a))) >>> second f >>> g first (Container f) = Container $ arr (\ ~(ws,~(x,y)) -> ((ws,x),y)) >>> first f instance ArrowLoop Container where loop (Container f) = Container $ loop (arr (\ ((ws,x),y) -> (ws,(x,y))) >>> f) The FG instances seem to match yours, except for ArrowLoop.