title: Why colons precede variables in Common Lisp
body: <p>What does the syntax, colons preceding variable in Common Lisp, mean? I've seen programs with such, and I'll present some sample code here, out of a large set of functions.</p>
  
  <pre><code>(defun expand (successorf node)
      (mapcar (lambda (action-state-cost)
            (let ((action (car action-state-cost))
                  (state (cadr action-state-cost))
                  (cost (caddr action-state-cost)))
              (make-node :state state :parent node
                         :action action :path-cost (+ (node-path-cost node) cost)
                         :depth (1+ (node-depth node)))
              ))
        (funcall successorf (node-state node))
        ))
  </code></pre>