Re: [Haskell-cafe] Can't figure out how to "show" for type "Int -> (Int, Int)"

On Thu, 11 Jan 2007, Tom Titchener wrote:

Here' my code:

data Term = Con Int | Div Term Term type M a = State -> (a, State) -- higher-order type, e.g. function type type State = Int -- type synonym eval :: Term -> M Int eval (Con a) x = (a, x) eval (Div t u) x = let (a, y) = eval t x in let (b, z) = eval u y in (a `div` b, z + 1) answer, error :: Term answer = (Div(Div(Con 1972)(Con 2))(Con 23)) error = (Div(Con 1)(Con 0))

I get the "ERROR" message when I type "eval answer" at the Hugs prompt.

'eval' requires two arguments, the second one is hidden in (M Int) which expands to (State -> (a, State)). That is, you must call eval answer 42 or so.