(Note, moved to haskell-cafe.)

Essentially, the answer is "yes", the state needs to be passed around (neglecting hackery to simulate global variables that is better avoided). However, this can be made convenient by using a monad.

BTW, Minh, If you don't know what monads are, then read this. Monads are an indispensable part of programming in Haskell: http://www.nomaware.com/monads/html/ http://haskell.org/hawiki/Monad Monads are good. Monads are your friend. Jared. -- http://www.updike.org/~jared/ reverse ")-:"