anchor.diff:  (defun expex-stack-locals? (ex)
     (and *expex-funinfo* ; Is set if we're inside a function.
   	   (transpiler-stack-locals? (expex-transpiler ex))))
  +
  +(defun expex-warn (x)
  +  (and *expex-warn?*
  +	   (symbolp x)
  +	   (not (or (functionp x)
  +				(keywordp x)
  +				(in? x nil t '~%ret 'this)
  +	   			(funinfo-in-this-or-parent-env? *expex-funinfo* x)
  +				(assoc x *variables*)
  +	       		(expander-has-macro? (transpiler-std-macro-expander *current-transpiler*) x)
  +		       	(expander-has-macro? (transpiler-macro-expander *current-transpiler*) x)))
  +	   (warn "symbol ~A is not defined in function ~A.~%"
  +			 (symbol-name x) (funinfo-get-name *expex-funinfo*))))
   
   ;;;; PREDICATES
   
  
positive.code: 
  ;; Expand arguments to function.
  (defun expex-argexpand-0 (ex fun args)
    (funcall (expex-function-collector ex) fun args)
    (let argdef (funcall (expex-function-arguments ex) fun)
  	(if (eq argdef 'builtin)
  
negative.code: ;;;;; assignments to temporary variables.
  
  (defvar *expex-funinfo* nil)
  (defvar *expex-warn?* nil)
  
  ;;;; CONFIGURATION
  
  