10 DEFINT A-Z: DATA "~",4,"&",3,"|",2,"^",2,"=>",1
20 DIM V(26),E(255),S(255),C(5),C$(5)
30 FOR I=1 TO 5: READ C$(I),C(I): NEXT
40 PRINT "Boolean expression evaluator"
50 PRINT "----------------------------"
60 PRINT "Operators are: ~ (not), & (and), | (or), ^ (xor), => (implies)."
70 PRINT "Variables are A-Z. Constant False and True are 0 and 1."
100 FOR I=1 TO 26: V(I)=0: NEXT
110 PRINT: LINE INPUT "Enter an expression: ";A$
120 E$="": E=0: S=0
130 FOR I=1 TO LEN(A$)
140 I$=MID$(A$,I,1)
150 IF I$<>" " THEN E$=E$+I$
160 NEXT
170 IF E$="" THEN END ELSE Y$=E$
180 IF E$="" THEN 330
190 A$=LEFT$(E$,1): A=ASC(A$) OR 32: B$=RIGHT$(E$,LEN(E$)-1)
200 IF A>=97 AND A<=122 THEN E(E)=A-33: E=E+1: E$=B$: GOTO 180
210 IF A$="0" OR A$="1" THEN E(E)=VAL(A$)+32: E=E+1: E$=B$: GOTO 180
220 IF A$="(" THEN S(S)=97: S=S+1: E$=B$: GOTO 180
225 IF A$=")" THEN E$=B$: GOTO 300
227 I=1
230 IF LEFT$(E$,LEN(C$(I)))=C$(I) THEN 250 ELSE I=I+1: IF I<6 THEN 230
240 PRINT "Parse error at: ";E$: PRINT: GOTO 100
250 A$=C$(I): E$=RIGHT$(E$,LEN(E$)-LEN(A$))
260 IF I=1 THEN S(S)=1: S=S+1: GOTO 180
270 IF S=0 THEN 290
275 IF S(S-1)<>97 AND C(S(S-1) AND 31)>=C(I) THEN 280 ELSE 290
280 S=S-1: E(E)=S(S): E=E+1: GOTO 270
290 S(S)=I: S=S+1: GOTO 180
300 IF S=0 THEN PRINT "Error: missing (!": GOTO 100
310 IF S(S-1)<>97 THEN S=S-1: E(E)=S(S): E=E+1: GOTO 300
320 S=S-1: GOTO 180
330 IF S=0 THEN 350 ELSE S=S-1
335 IF S(S)=97 THEN PRINT "Error: missing )!": GOTO 100
340 E(E)=S(S): E=E+1: GOTO 330
350 V$=""
360 FOR I=0 TO E-1
370 IF (E(I) AND 224)<>64 THEN 390
380 A$=CHR$(E(I)+1): IF INSTR(V$,A$)=0 THEN V$=V$+A$
390 NEXT
400 GOSUB 600
410 FOR I=1 TO LEN(V$): PRINT MID$(V$,I,1);" ";: NEXT
420 PRINT "| ";Y$
430 PRINT STRING$(2+2*LEN(V$)+LEN(Y$),"-")
440 FOR J=1 TO 2^LEN(V$)
450 FOR I=1 TO LEN(V$)
460 IF V(I) THEN PRINT "T "; ELSE PRINT "F ";
470 NEXT
480 PRINT "| ";: GOSUB 600: IF S(0) THEN PRINT "T" ELSE PRINT "F"
490 I=1
500 IF V(I) THEN V(I)=0: I=I+1: GOTO 500 ELSE V(I)=1
510 NEXT
520 GOTO 100
600 S=0
610 FOR I=0 TO E-1: T=E(I) AND 224: V=E(I) AND 31
620 IF T=0 THEN ON V GOTO 700,710,720,730,740
630 IF T=32 THEN S(S)=-V: S=S+1: GOTO 650
640 IF T=64 THEN S(S)=V(INSTR(V$,CHR$(V+65))): S=S+1: GOTO 650
650 NEXT
660 IF S<>1 THEN PRINT "Missing operator": GOTO 100
670 RETURN
700 IF S<1 THEN 770 ELSE S(S-1)=1-S(S-1): GOTO 650
710 IF S<2 THEN 770 ELSE S=S-1:S(S-1)=S(S-1) AND S(S): GOTO 650
720 IF S<2 THEN 770 ELSE S=S-1:S(S-1)=S(S-1) OR S(S): GOTO 650
730 IF S<2 THEN 770 ELSE S=S-1:S(S-1)=S(S-1) XOR S(S): GOTO 650
740 IF S<2 THEN 770 ELSE S=S-1
750 IF S(S-1) THEN S(S-1)=S(S) ELSE S(S-1)=-1
760 GOTO 650
770 PRINT "Missing operand": GOTO 100