title: How to create a binary stream (not a file) in Common Lisp?
body: <p>I have a function which output some binary data to a stream. But the stream is abstract, which means the stream can be a file stream, or some other streams. But the stream must be a binary stream which support write-byte function. I searched but not found the answer.</p>
  
  <p>What I want to do is, I have a function which will convert some data to a gif. But I donot want to output the data to a file, I want to output it to something in memory. </p>
  
  <p>Thanks.</p>