Fibonacci in Haskell

fib.hs

fib :: Int -> Int
fib x
    | x < 0 = error ("Can't calculate fib of negative number " ++ show x)
    | x == 0 = 0
    | x > 0 = accum (x-1) 0 1
        where
            accum :: Int -> Int -> Int -> Int
            accum x y z
                | x > 0 = accum (x-1) z (y+z)
                | otherwise = z

main = print [(x,fib x) | x <- [0..9]]

Flexing my functional muscle.