[lisp-snmp] Patch to asn.1 to change from parsergen to a modified cl-yacc

[John F. <jf...@ms...>]

And if anybody is interested in converting from parsergen syntax to
cl-yacc syntax, here are some helper functions

(defun defparser-production-to-yacc (grammar-symbols forms)
  (cond ((not (and forms (or (not (listp forms)) (some 'identity forms))))
	 nil)
	(t
	 (labels ((make-var (i)
		    (intern (format nil "$~D" i)))
		  (vars ()
		    (loop for i from 1 for x in grammar-symbols collect (make-var i)))
		  (used-vars ()
	     (remove-duplicates  
	      (loop for sym in (alexandria:flatten forms)
		    when (and (symbolp sym) (eql #\$ (elt (symbol-name sym) 0))
			      (ignore-errors (parse-integer (symbol-name sym) :start 1)))
		    collect (make-var (parse-integer (symbol-name sym) :start 1)))
	      :test 'eql)))
	   (let ((unused-vars (set-difference (vars) (used-vars))))
	     (list `#'(lambda(,@(vars)) 
		   ,@(when unused-vars  (list `(declare (ignore ,@unused-vars))))
		   ,forms)))))))

(defun defparser-to-yacc (rules)
  (let (grouped-rules)
    (loop for rule in rules do
	  (destructuring-bind ((non-terminal &rest grammar-symbols) &optional forms)
	      rule
	    (assert non-terminal)
	    (push (append grammar-symbols (defparser-production-to-yacc grammar-symbols forms)) 
		  (sys:cdr-assoc non-terminal grouped-rules))))
    (loop for (name . alternatives) in (nreverse grouped-rules)
	  collect `(,name ,@(reverse alternatives)))))