anchor.diff:  ;;;
   ;;; Converting quote
   
  +(define-condition quote-must-have-a-single-argument
  +    (compilation-program-error)
  +  ())
  +
   (defmethod convert-special ((op (eql 'quote)) ast environment)
  -  (assert (= (length (children ast)) 2))
  +  (unless (= (length (children ast)) 2)
  +    (error 'quote-must-have-a-single-argument
  +	   :form (form ast)))
     (make-instance 'constant-ast
   		 :form (form ast)
   		 :value (cadr (children ast))))
  
positive.code:   ())
  
  (defmethod convert-special ((op (eql 'setq)) ast environment)
    ;; FIXME check if the length is odd
    (assert (= (length (children ast)) 3))
    ;; FIXME check ever other argument
    (assert (typep (car (children ast)) 'symbol-ast))
    ;; FIXME: issue a warning if the variable doesn't exist 
    ;; FIXME: turn it into a progn of setqs with two args. 
    (make-instance 'setq-ast
  
negative.code: 					      :value nil)
  			       (convert (cadddr (children ast)) environment))))
  
  