1) Haven't look closely, but your second ArrowLoop instance seems righter. The
question really is the same as with MonadFix instances; you can always define
an instance like this
data M = ... -- whatever
instance Monad M where ...
instance MonadFix M where mfix f = mfix f >>= f
...but this generally won't do any good.
Maciej Piechotka wrote:
Hello. I'm trying to understand the FRP (by implementing FRP system on
my own) and I think I'm slowly getting it.
1. How to interpret ArrowLoop? I have two possible implementations:
type RunSF a = a Dynamic ()
data SF a b c =
SF (a (Dynamic, b, RunSF, Set Unique) (c, Set Unique, SF a b c))
(...)
instance ArrowLoop (SF a) where
loop (SF f) = loop' f undefined
where loop' g d = proc (dyn, b, r, s) -> do
((c, d'), s, g') <- g <- (dyn, (b, d), r, s)
returnA -< (c, s, loop' g' d')
instance ArrowLoop a => ArrowLoop (SF a) where
loop (SF f) = SF $! proc (d, b, r, s) -> do
rec ((c, d), s, f') <- f -< (d, (b, d), r, s)
returnA -< (c, s, loop f')
Since the first is not unlike ArrayCircuit from arrays I guess second
one but I'm not quite sure.
2. Why there is no ArrowIO in arrows? I.e.
class Arrow a => ArrowIO a where
liftAIO :: Kleisli IO b c -> a b c
(possibly
class Arrow a => ArrowST a where
liftAST :: Kleisli ST b c -> a b c
)
3. Why switch is needed? How to interpret switch with current
continuation?
I think switch is equivalent to ArrowChoice but do I miss something?
Regards
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