;; C311 Programming Laguages
;; Fall 2008
;; Dana Vrajitoru

;; Evaluation functions for the grammar that recognizes an arithmetic
;; expression. This version returns the value of subtrees that cannot
;; be evaluated by themselves as a lambda expression.


(load-file "parse_expr.el")

; To be able to test the others I made this return something for now.
(defun eval2-E (Tree) 
  (let ((Tres (eval2-T (elt Tree 1))) 
	(TTres (eval2-TT (elt Tree 2))))
    (funcall TTres Tres)))

; To be able to test the others I made this return something for now.
(defun eval2-T (Tree) 2)

;; '(TT) when it expands to e.
;; '(TT (AO "+") (T ...) (TT ...))
(defun eval2-TT (Tree)
  (if (or (not Tree)
	  (not (equal (car Tree) 'TT)))
      nil
    (if (equal (length Tree) 1)
	(lambda (x) x)
      (let ((Tres (eval2-T (elt Tree 2))) 
	    (TTres (eval2-TT (elt Tree 3)))
	    (Res 0))
	(setq Res (funcall TTres Tres))
	(cond ((equal (cadr (cadr Tree)) "+")
	       (append '(lambda (x)) (list (list '+ 'x Res))))
	      ((equal (cadr (cadr Tree)) "-")
	       (append '(lambda (x)) (list (list '- 'x Res))))
	      (t nil))))))

(eval2-TT '(TT (AO "+") (T "...") (TT)))
(lambda (x) (+ x 2))



; '(F 2)
; '(F a)
; '(F "(" (E ...) ")")
(defun eval2-F (Tree)
  (if (or (not Tree)
	  (not (equal (car Tree) 'F)))
      nil
    (if (= (length Tree) 2) ; number or symbol
	(eval (cadr Tree))
      (eval2-E (elt Tree 2)))))

(eval2-F '(F 2))
2
(setq a 5)
5
(eval2-F '(F a))
5
(eval2-F '(F "(" (E (T) (TT)) ")" ))
2



; Parses the list of tokens and build a parse tree, then calls the
; evaluation of the tree and returns the value.
((defun process (L)
  (let ((Tree (parse-input L)))
    (if (not Tree) nil
      (princ "The parse tree is:\n")
      (prin1 Tree)
      (princ "\nThis is evaluated to\n")
      (eval2-E Tree))))