I think that's a fine assertion to make, because Haskell functions can die at runtime because of pattern match failure or an explicit evaluation of "bottom" (undefined).

    Prelude> undefined
    *** Exception: Prelude.undefined

    Prelude> let x 2 = 4 in x 1
    *** Exception: <interactive>:7:5-11: Non-exhaustive patterns in function x

Neither of these behaviors is indicated in the type definition:

    Prelude> :t undefined
    undefined :: t

    Prelude> :t let x 2 = 4 in x
    let x 2 = 4 in x :: (Eq a, Num a, Num a1) => a -> a1

I was promised a -> a but got a runtime exception instead.