Re: [Haskell-cafe] Coroutines

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" wrote:

On Thu, Dec 18, 2008 at 2:00 AM, Nicolas Pouillard 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" _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe