title: Determining if a number is negative in Scheme with one function
body: <p>I have been going through The Little Schemer and I started getting curious about how to deal with negative numbers.  It seemed like a nice challenge to figure out how to build a function to determine if a number is negative or positive.</p>
  
  <p>So far I have this solution:</p>
  
  <pre><code>(define negative?
    (lambda (a)
      (cond
        ((zero? a) #f)
        (else (negativeHelper (sub1 a) (add1 a))))))
  
  (define negativeHelper
    (lambda (a b)
      (cond
        ((zero? a) #f)
        ((zero? b) #t)
        (else (negativeHelper (sub1 a) (add1 b))))))
  </code></pre>
  
  <p>This looks to be working nicely, but my question is if it is possible to right <code>negative?</code> without the helper function?</p>