title: "unbound identifier in module" error in Racket
body: <p>I'm writing a function in Racket, using DrRacket:</p>
  
  <pre><code>(define (same-parity a .b)
   (let ((remain (remainder a 2)))
    (define (recur-part remain-list)
     (cond ((= remain (remainder (car remain-list) 2))
           (append remain-list (list (car remain-list)))
           (recur-part (cdr remain-list)))
          (else (recur-part (cdr remain-list)))))
    (recur-part b)))
  </code></pre>
  
  <p>But the compiler complains the following:<code>b: unbound identifier in module in: b</code></p>
  
  <p>How could it be for the <code>(recur-part b)</code> is in the scope of the definition of <code>same-parity</code>?</p>
  
  <p>Thanks!</p>