;;;-*- Mode: Common-Lisp; Base:10; Package: tiger -*-
;; set up for johnson-yacc parser

;;; ----- Example grammars -----

(def-jyacc week7
  (P  ([ S ]* $)   `(progn . ,%0))
  (S  (print E \;) `(format t "~a~%" ,%1))
  (S  (id = E \;)  `(setf ,%0 ,%2)) 
  (S  (E $) %0)
  (E  (E + Tm or E - Tm) `(,%1 ,%0 ,%2))
  (E  (Tm))
  (Tm (Tm * F or Tm / F) `(,%1 ,%0 ,%2))
  (Tm (F))
  (F  (id or num))
  (F  (|(| E |)|)  %1))

(defun parse-week7 (tokens)
  ;; parse from a list of tokens, e.g. ( (id x) + (id y) $)
  (labels ((next() 
             (let ((h (pop tokens)))
               (cond
                 ((null h)    '(*eof* . *eof*)) ; If we're at EOF
                 ((numberp h) `(num . ,h))
                 ((eq h 'print) '(print . print))
                 ((and (symbolp h) (alpha-char-p (elt (symbol-name h) 0)))
                  `(id . ,h))
                 ((atom h) (cons h h))       ; If it's a +, return (+ . +)
                 (t (cons (car h) h)))))
           (err() (format t "~%error at ~s" tokens)))
    (week7 #'next #'err)))

;; Example: (parse-week7 '(a = 1 + 7 \; b = a * a \; print b - a \; $))