LISP - converting grammar inputs to strings (language theory)

Question

I have implemented a problem which determines the non-productive or inaccessible elements from a Grammar (Vn;Vt;P;S) where Vn - set of variables; Vt- set of terminals and P - production rules, and S - start symbol.

; Defining a grammar
(defvar *VN* '(A B C D S)) ; non-terminal variables
(defvar *VT* '(k m n)) ; terminal
(defvar *P* '((S A B) ; set of production rules
    (S C D)
    (S A k)
    (A k)
    (B m)
    (B D m D)
    (C n)
    )
)

;;; FINDING PRODUCTIVE ELEMENTS
(defun PROD-STEP (VT P PRODS)
    ;(format t "P = ~S~%" P)
    ;(format t "PRODS = ~S~%" PRODS)
    (if (null P) PRODS
        (if (subsetp (rest (first P)) (union VT PRODS))
            (PROD-STEP VT (rest P) (union (cons (first (first P)) nil) PRODS))
            (PROD-STEP VT (rest P) PRODS)
        )
    )
)
(defun PROD-AUX (VT P PRODS oldLength)
    (if (= (length PRODS) oldLength)
        PRODS
        (PROD-AUX VT P (PROD-STEP VT P PRODS) (length PRODS))
    )
)

(defun PROD (VT P)
    (PROD-AUX VT P nil -1)
)
;;; END OF FINDING PROD ELEMENTS

(trace PROD-STEP)
(trace PROD-AUX)
(trace PROD)
(PROD *VT* *P*)


;;; FINDING ACCESSIBLE ELEMENTS
(defun ACCESS-STEP (P ACC)
    ;(format t "Pacc = ~S~%" P)
    ;(format t "ACC = ~S~%" ACC)
    (if (null P) ACC
        (if (member (first (first P)) ACC)
            (ACCESS-STEP (rest P) (union (rest (first P)) ACC))
            (ACCESS-STEP (rest P) ACC)
        )
    )
)

(defun ACCESS-AUX (P ACC oldLength)
    (if (= (length ACC) oldLength)
        ACC
        (ACCESS-AUX P (ACCESS-STEP P ACC) (length ACC))
    )
)
(defun ACCESS (P S)
    ;(format t "Paccess = ~S~%" P)
    (ACCESS-AUX P (cons S nil) 0)
)
 ;;; END OF FINDING ACCESSIBLE ELEMENTS

(trace ACCESS-STEP)
(trace ACCESS-AUX)
(trace ACCESS)
(ACCESS *P* 'S)

;;; REMOVING INACCESSIBLE AND NOT PRODUCTIVE ELEMENTS
(defun BuildRules-AUX (VT ACCS PRODS P newP)
    ;(format t "newP = ~S~%" newP)
    (if (null P) newP
        ; VN' = (ACCESS(G) INTERSECT PROD(G))
        ; VT' = (VT INTERSECT ACCESS(G))
        ; DACA REGULA ESTE A->X, A = (first (first P)) SI X = (rest (first P))
        ; VERIFICAM DACA A APARTINE VN' SI X APARTINE (VT' UNION VN')
        (if (and (member (first (first P)) (intersection PRODS ACCS)) (subsetp (rest (first P)) (union (intersection ACCS PRODS) (intersection VT ACCS)) ))
            (BuildRules-AUX VT ACCS PRODS (rest P) (union newP (cons (first P) nil)))
            (BuildRules-AUX VT ACCS PRODS (rest P) newP)
        )
    )   
)

(defun BuildRules (VT ACCS PRODS P)
    (BuildRules-AUX VT ACCS PRODS P nil)
)
(trace BuildRules-AUX)
(trace BuildRules)

(BuildRules *VT* (ACCESS *P* 'S) (PROD *VT* *P*)*P*)

(defun SIMPL-AUX (VN VT P S ACCS PRODS)
    (setq ACCS (ACCESS P S))
    (setq PRODS (PROD VT P))
    (if (and (null (set-difference (union VN VT) ACCS)) (null (set-difference VN PRODS)))
        (cons VN (cons VT (cons P S)))
        (SIMPL-AUX 
                    (intersection ACCS PRODS)
                    (intersection VT ACCS)
                    (BuildRules VT ACCS PRODS P)
                    S
                    ACCS
                    PRODS
        )
    )
)
(defun SIMPL (VN VT P S)
    (SIMPL-AUX *VN* *VT* *P* 'S nil nil)
)
;;; END OF REMOVING INACCESSIBLE AND NOT PRODUCTIVE ELEMENTS

;;; GETTING THE RESULTS
  (SIMPL *VN* *VT* *P* 'S)

The program is working as expected, the only question i would like to ask how to convert the input data into strings as i would like to make difference between "a" terminal and "A" non-terminal.

I suppose i should use something like that as in input "a", "k", "*", "begin" etc..

Thank you in advance...

Answer 1

you can use symbols: |this is still a Symbol, which keeps its case|

|m| and M are both symbols. Different symbols.