anchor.diff:  			:literal form :types '((body))))
   	  ((symbolp form)		;function call
   	   (compile-funcall form))
  -	  (t (bst-compile-error "Illegal form in BST function body: ~S" form)))))))
  +	  (t (bst-compile-error "Illegal form in BST function body: ~:S" form)))))))
   
   (defun bst-compile-defun (name function-definition)
     "Compile a BST wizard-defined function of given NAME and
  
positive.code: 
        ;; First pass: compute the arity of both branches
        (multiple-value-bind (else-form else-arg-types else-res-types else-side-effects)
  	  (let ((*lexicals* ())) ; don't introduce local lexical bindings
  	    (bst-compile-literal else-literal ()))
  ;;(format t "~&;; else-form ~S is ~S --> ~S~%" else-literal else-arg-types else-res-types)
  	(multiple-value-bind (then-form then-arg-types then-res-types then-side-effects)
  	    (let ((*lexicals* ())) ; don't introduce local lexical bindings
  	      (bst-compile-literal then-literal ()))
  ;;(format t "~&;; then-form ~S is ~S --> ~S~%" then-literal then-arg-types then-res-types)
  	  ;; Introduce lexical binding for the union of all
  	  ;; assigned-to variables in both branches.
  	  (let ((assigned-variables
  
negative.code:     
  
  (defun bst-compile-warning (format-string &rest args)
    (unless *silent-compilation*
      (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
  