Re: [Haskell-beginners] State monad

On Mon, Feb 14, 2011 at 8:11 PM, Britt Anderson wrote:

Many of the tutorials on the state monad seem to suggest that you can use State as a data constructor, but I can't get this to work. E.g. in ghci after :m Control.Monad.State I can

let f = (\x -> (x,x)) let y = state f

but if I,

let z = State f

I get an error message: Not in scope: data constructor `State'.

Can someone please explain?

Thanks, Britt

GHCi doesn't load all Haskell modules by default. It only loads Prelude. You'll have to load them by hand. Use :m +Control.Monad.State -- Mihai