But in a way, imperative is more natural, because it captures the notion of computation more precisely. Haskell -- like other pure FP languages -- is built around the approximation of denotational semantics, which does have a bit of a mismatch with computation (not to say it isn't extremely useful much of the time). Anyway, mathematical thinking about programs didn't start with PFP, nor is PFP the most common way of formalizing programs. See:

http://research.microsoft.com/en-us/um/people/lamport/pubs/s...

I believe that the best way to get better programs is to teach programmers how to think better. Thinking is not the ability to manipulate language; it’s the ability to manipulate concepts. Computer science should be about concepts, not languages. But how does one teach concepts without getting distracted by the language in which those concepts are expressed? My answer is to use the same language as every other branch of science and engineering—namely, mathematics.

It makes me sad that some PFP enthusiasts enjoy the mathematical aspects of it -- as they should -- yet are unfamiliar with the more "classical" mathematical thinking. I think it's important to grasp the more precise mathematics first, and only then choose which approximations you'd make in the language of your choice. Otherwise you get what Lamport calls "Whorfian syndrome — the confusion of language with reality".