anchor.diff:         (nconc (nreverse front) (cons '====> body)))
       (setq front (cons (car body) front))))
       
  +
  +(defun bst-compile-warning (format-string &rest args)
  +  (signal (make-condition 'bst-compiler-warning
  +			  :message
  +			  (concatenate 'string
  +				       (format nil " In BST body ~S:~%  "
  +					       (currently-compiled-body-with-markup))
  +				       (apply 'format nil format-string args)))))
   
   (defun bst-compile-error (format-string &rest args)
     (error (make-condition 'bst-compiler-error
  
positive.code: 				   :assigned-variables (list assigned-thing)
  				   :unconditionally-assigned-variables (list assigned-thing)))))
  	  (cond
  	    ((setq assoc (assoc name *lexical-variables* :test 'string-equal))
  	     (let ((var-name (variable-name (cdr assoc)))
  		   (value-mvform (pop-single-value-form t :need-variable nil)))
  
negative.code: 	     (let* ((setter-form-maker (bst-function-setter-form-maker fun))
  		    (value-mvform (pop-single-value-form t :need-variable nil))
  		    (setter-form (funcall setter-form-maker (mvform-form value-mvform))))
  	       (incf (bst-function-num-assignments fun))
  	       (setf (bst-function-assigned-value-form fun) (mvform-form value-mvform))
  	       (push-mvform
  		:form setter-form :types ()
  		:side-effects (compute-side-effects name value-mvform)))))))))
  