title: representing infinity and NAN independent of implementation
body: <p>Is there an implementation independent way of representing infinity or not a number (NAN) in Common Lisp? It would need to be a double float, and have both positive and negative values. In SBCL, the results of</p>
  
  <pre><code>(apropos "INFINITY")
  </code></pre>
  
  <p>include</p>
  
  <pre><code>SB-EXT:DOUBLE-FLOAT-NEGATIVE-INFINITY (bound)
  SB-EXT:DOUBLE-FLOAT-POSITIVE-INFINITY (bound)
  </code></pre>
  
  <p>but I need it to be available in all implementations. I have an addendum to a package to write that runs on all platforms and it needs a representation of infinity and NAN. Even functions from another library would suffice.</p>
  
  <p>I got <code>iee-floats</code> loaded and it's a part of my library now. I have a function that detects if a number is NaN and one that detects whether a number is infinity; I haven't tested NaN out but my infinity function needs the number to be a double-float. SBCL's <code>SB-EXT:DOUBLE-FLOAT-POSITIVE-INFINITY</code> works but I would need it to be implementation independent.</p>