On May 21, 2010, at 3:51 AM, Brent Yorgey wrote:
On Thu, May 20, 2010 at 11:53:09AM +1200, Richard O'Keefe wrote:
On May 20, 2010, at 3:18 AM, Brent Yorgey wrote:
On Wed, May 19, 2010 at 04:27:14AM +0000, R J wrote:
What are some simple functions that would naturally have the following type signatures: f :: (Integer -> Integer) -> Integer
The key point is the 'that would NATURALLY have', which I take to mean "as a result of type inference without any forcibly imposed type signatures".
Given that this is an exercise in Chapter 1, I kind of doubt this is really what it is supposed to mean. Are people reading chapter 1 really expected to understand the intricacies of type inference and the Num class? And to know about 'toInteger' and the fact that numeric constants are polymorphic? I really doubt it. I read the question much more simply, with "naturally" having a much more informal meaning than you suggest. I interpret the question as simply getting the reader some practice with basic higher-order types.
The other possibility, of course, is a setup where Integer is the default type, so the function should just be f g = g 0 + 0. But "naturally" has to mean *something*, and the questions are clearly about type inference.