Suppose I had a language that had only one kind of speech act: promising. Could I communicate information in the way we do in assertion? Yes! For, suppose I want to communicate that it's raining. Then I could say "I promise to immediately exclaim 'just kidding!' unless it's raining" without exclaiming "just kidding!"
We could even imagine that over time this would get abbreviated to: "It's raining."
Thus, one can reduce assertion, or something very much assertion-like, to promising. Moreover, if we say that this really is normatively equivalent to assertion, then we get an account of the wrongness of lying and a reduction of the normativity of assertion to moral normativity.
One cannot, however, reduce all speech acts to promises. For while promises generate reasons for self, requests (including questions) and commands generate reasons for others.