In my opinion, in Haskell, you don't need coroutines because you have
lazy evaluation.
You example below is simply an example of a heterogenous list being
read. The simplest way to implement a heterogenous list in Haskell is
to use a tuple. Or you could use the HList package.
--
Robin
On Thu, 18 Dec 2008 02:26:26 -0800
"Ryan Ingram" <ryani.s...@gmail.com> wrote:
> On Thu, Dec 18, 2008 at 2:00 AM, Nicolas Pouillard
> <nicolas.pouill...@gmail.com> wrote:
> > I don't see why one would need session types, channels... to
> > express that. I maybe need a more complicated coroutines (ruby)
> > example that would require using this system.
>
> OK, how would you type these routines in Haskell?
>
> def simple
> yield "hello"
> yield 1
> yield (lambda { |x| x + 1 })
> end
>
> def useSimple
> state = 0
> result = nil
> simple { |x|
> if (state == 0) then result = x
> else if (state == 1) then result += (x * 4).toString
> else if (state == 2) then result += x.call(10).toString
> state = state + 1
> }
> result
> end
>
> I know it's a bit contrived, but you get the idea.
>
> In Haskell using Control.Coroutine:
>
> simple :: forall rest. Session (String :!: Int :!: (Int -> Int) :!:
> rest) rest ()
> simple = do
> put "hello"
> put 1
> put (\x -> x + 1)
>
> useSimple :: forall rest. Session (String :?: Int :?: (Int -> Int) :?:
> rest) rest String
> useSimple = do
> string <- get
> int <- get
> func <- get
> return (string ++ show (int * 4) ++ show (func 10))
>
> result :: String
> result = snd $ connects simple useSimple
> -- result = "hello411"
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