Asfand Yar Qazi wrote:
> I'm trying to implement hierarchical states in Haskell, following on from my
> work at doing them in C++.
>
> Here's what I've got so far:
>
> data StateNode a = CompositeState [ StateNode a ] | State a
> stateslist :: StateNode a -> [a]
> stateslist(State x) = [x]
> stateslist(CompositeState xs) = {- return list of objects of type a -}
>
> The following give errors (as they should)
> -- stateslist(CompositeState xs) = [ stateslist(x) | x <- xs ]
> -- stateslist(CompositeState xs) = map stateslist xs
>
> You see what I'm trying to do? This is how I want it to behave:
>
> sm1 = CompositeState [ State 1, State 2, State 3 ]
> stateslist(sm1)
> => [1, 2, 3]
Maybe...
stateslist :: StateNode a -> [a]
stateslist (State x) = [x]
stateslist (CompositeState xs) = concatMap stateslist xs
Greg Buchholz
_______________________________________________
Haskell mailing list
Haskell@haskell.org
http://www.haskell.org/mailman/listinfo/haskell
