On Thu, Dec 16, 2010 at 06:52:58PM +0100, Yves Parès wrote:
Okay, I started to experiment things, and I came to some remarks: First, I cannot use bare lists, because of the way their Applicative instance is declared. I have to use the newtype ZipList (in Control.Applicative). So I have roughly this :
import Control.Applicative
newtype AgentSig a = AgentSig (ZipList a) deriving (Functor, Applicative)
(<+>) :: a -> AgentSig a -> AgentSig a v <+> (AgentSig (ZipList sig)) = AgentSig . ZipList $ v:sig
toList :: AgentSig a -> [a] toList (AgentSig (ZipList sig)) = sig
fromList :: [a] -> AgentSig a fromList = AgentSig . ZipList
This enables me to do things like : agent3 a b = (/) <$> a <*> b run = z where x = agent1 y y = 100 <+> agent2 x z = agent3 x y
One problem though: How to make an instance of Monad out of AgentSig?
You can make a monad instance out of AgentSig as long as AgentSig always contains an infinite list (otherwise the monad laws are not satisfied). It is based on the idea of "diagonalization". instance Monad AgentSig where return = fromList . repeat (AgentSig (ZipList xs)) >>= f = fromList $ diag (map (toList . f) xs) where diag ((y:_):zs) = y : diag (map tail zs) So in the result of (a >>= f), the first element is taken from the first element of applying f to the first element of a; the second element is the second element in the result of applying f to the second element of a; and so on. Off the top of my head I am not sure what this corresponds to in terms of agents or where it would be useful, but I'm sure it must correspond to something interesting. -Brent