DECLARE SUB LLISTSTMT ()
DECLARE SUB LPRINTSTMT ()
DECLARE SUB INITGETSYM (N AS INTEGER)
DECLARE SUB VALIDLINENUM ()
DECLARE SUB DOCMD ()
DECLARE SUB CLEARVARS ()
DECLARE SUB LISTSTMT ()
DECLARE SUB GOTOSTMT ()
DECLARE SUB IFSTMT ()
DECLARE SUB INPUTSTMT ()
DECLARE SUB PRINTSTMT ()
DECLARE SUB SKIPTOEOL ()
DECLARE SUB IDSTMT ()
DECLARE SUB GETSYM ()
DECLARE SUB EXPECT (S AS STRING)
DECLARE SUB GOTOLINE ()
DECLARE FUNCTION EXPRESSION% ()
DECLARE FUNCTION ADDEXPR% ()
DECLARE FUNCTION TERM% ()
DECLARE FUNCTION FACTOR% ()
DECLARE FUNCTION GETVARINDEX% ()
DECLARE FUNCTION ACCEPT% (S AS STRING)
DECLARE SUB GETCH ()
DECLARE SUB READSTR ()
DECLARE SUB READIDENT ()
DECLARE SUB READINT ()

DIM SHARED CH$, THELIN$, PGM$(2000), TOK$


DIM SHARED VARS(26) AS INTEGER, CURLINE AS INTEGER, NUM AS INTEGER
DIM SHARED TEXTP AS INTEGER, ERRORS AS INTEGER


DO
ERRORS = 0
LINE INPUT "> ", PGM$(0)
IF PGM$(0) <> "" THEN
CALL INITGETSYM(0)
IF LEFT$(TOK$, 1) >= "0" AND LEFT$(TOK$, 1) <= "9" THEN
CALL VALIDLINENUM
PGM$(NUM) = MID$(PGM$(0), TEXTP, LEN(PGM$(0)) - TEXTP + 1)
ELSE
CALL DOCMD
END IF
END IF
LOOP

FUNCTION ACCEPT% (S AS STRING)
ACCEPT% = 0
IF TOK$ = S THEN ACCEPT% = 1: CALL GETSYM
END FUNCTION

FUNCTION ADDEXPR%
DIM N
N = TERM%
ADDEL:
IF TOK$ = "+" THEN CALL GETSYM: N = N + TERM%: GOTO ADDEL
IF TOK$ = "-" THEN CALL GETSYM: N = N - TERM%: GOTO ADDEL
ADDEXPR% = N
END FUNCTION

SUB CLEARVARS
DIM I AS INTEGER
FOR I = 1 TO 26
VARS(I) = 0
NEXT I
END SUB

SUB DOCMD
DIM I AS INTEGER
AGAIN:
IF ERRORS <> 0 THEN EXIT SUB
WHILE TOK$ = ""
IF CURLINE = 0 OR CURLINE >= 1999 THEN EXIT SUB
CALL INITGETSYM(CURLINE + 1)
WEND
IF ACCEPT("STOP") OR ACCEPT("END") THEN EXIT SUB
IF ACCEPT("NEW") THEN
CALL CLEARVARS
FOR I = 1 TO 1999
PGM$(I) = ""
NEXT I
EXIT SUB
END IF
IF ACCEPT("BYE") THEN END
IF ACCEPT("LIST") THEN CALL LISTSTMT: GOTO AGAIN
IF ACCEPT("LLIST") THEN CALL LLISTSTMT: GOTO AGAIN
IF ACCEPT("RUN") THEN
CALL CLEARVARS
CALL INITGETSYM(1)
GOTO AGAIN
END IF
IF ACCEPT("GOTO") THEN CALL GOTOSTMT: GOTO AGAIN
IF ACCEPT("IF") THEN CALL IFSTMT: GOTO AGAIN
IF ACCEPT("INPUT") THEN CALL INPUTSTMT: GOTO AGAIN
IF ACCEPT("PRINT") THEN CALL PRINTSTMT: GOTO AGAIN
IF ACCEPT("LPRINT") THEN CALL LPRINTSTMT: GOTO AGAIN
IF ACCEPT("REM") THEN CALL SKIPTOEOL: GOTO AGAIN
IF LEFT$(TOK$, 1) >= "A" AND LEFT$(TOK$, 1) <= "Z" THEN
CALL IDSTMT
GOTO AGAIN
END IF
PRINT "UNKNOWN TOKEN "; TOK$; " AT LINE "; CURLINE
END SUB

SUB EXPECT (S AS STRING)
IF ACCEPT(S) <> 0 THEN EXIT SUB
ERRORS = 1
PRINT "EXPECTING "; S; " BUT FOUND "; TOK$
END SUB

FUNCTION EXPRESSION%
DIM N
N = ADDEXPR%
EXPRL:
IF TOK$ = "=" THEN CALL GETSYM: N = N = ADDEXPR%: GOTO EXPRL
IF TOK$ = "<" THEN CALL GETSYM: N = N < ADDEXPR%: GOTO EXPRL
IF TOK$ = ">" THEN CALL GETSYM: N = N > ADDEXPR%: GOTO EXPRL
IF TOK$ = "<>" THEN CALL GETSYM: N = N <> ADDEXPR%: GOTO EXPRL
IF TOK$ = "<=" THEN CALL GETSYM: N = N <= ADDEXPR%: GOTO EXPRL
IF TOK$ = ">=" THEN CALL GETSYM: N = N >= ADDEXPR%: GOTO EXPRL
EXPRESSION% = N
END FUNCTION

FUNCTION FACTOR%
IF ACCEPT("-") THEN
FACTOR% = -FACTOR%
EXIT FUNCTION
END IF
IF ACCEPT("(") THEN
FACTOR% = EXPRESSION
CALL EXPECT(")")
EXIT FUNCTION
END IF
IF LEFT$(TOK$, 1) >= "0" AND LEFT$(TOK$, 1) <= "9" THEN
FACTOR% = NUM
CALL GETSYM
EXIT FUNCTION
END IF
IF LEFT$(TOK$, 1) >= "A" AND LEFT$(TOK$, 1) <= "Z" THEN
FACTOR% = VARS(GETVARINDEX)
EXIT FUNCTION
END IF
PRINT "UNEXPECTED SYM "; TOK$; " IN FACTOR": ERRORS = 1
END FUNCTION

SUB GETCH
IF TEXTP > LEN(THELIN$) THEN CH$ = "": EXIT SUB
CH$ = MID$(THELIN$, TEXTP, 1)
TEXTP = TEXTP + 1
END SUB

SUB GETSYM
TOK$ = ""
WHILE CH$ <= " "
IF CH$ = "" THEN EXIT SUB
CALL GETCH
WEND


TOK$ = CH$
IF INSTR(",;=+-*/()", CH$) > 0 THEN CALL GETCH: EXIT SUB
IF CH$ = "<" THEN
CALL GETCH
IF CH$ = "=" OR CH$ = ">" THEN
TOK$ = TOK$ + CH$
CALL GETCH
END IF
EXIT SUB
END IF
IF CH$ = ">" THEN
CALL GETCH
IF CH$ = "=" THEN TOK$ = TOK$ + CH$: CALL GETCH
EXIT SUB
END IF
IF CH$ = CHR$(34) THEN CALL READSTR: EXIT SUB
IF CH$ >= "A" AND CH$ <= "Z" THEN CALL READIDENT: EXIT SUB
IF CH$ >= "0" AND CH$ <= "9" THEN CALL READINT: EXIT SUB
PRINT "WHAT->"; CH$: ERRORS = 1
END SUB

FUNCTION GETVARINDEX%
IF LEFT$(TOK$, 1) < "A" OR LEFT$(TOK$, 1) > "Z" THEN
PRINT "NOT A VARIABLE": ERRORS = 1: EXIT FUNCTION
END IF
GETVARINDEX% = ASC(LEFT$(TOK$, 1)) - ASC("A")
CALL GETSYM
END FUNCTION

SUB GOTOLINE
CALL VALIDLINENUM
CALL INITGETSYM(NUM)
END SUB

SUB GOTOSTMT
IF LEFT$(TOK$, 1) >= "0" AND LEFT$(TOK$, 1) <= "9" THEN
CALL GOTOLINE
EXIT SUB
END IF
PRINT "LINE NUMBER MUST FOLLOW GOTO": ERRORS = 1
END SUB

SUB IDSTMT
DIM VAR AS INTEGER
VAR = GETVARINDEX
CALL EXPECT("=")
VARS(VAR) = EXPRESSION
END SUB

SUB IFSTMT
DIM B AS INTEGER
IF EXPRESSION = 0 THEN CALL SKIPTOEOL: EXIT SUB
B = ACCEPT("THEN")
IF LEFT$(TOK$, 1) >= "0" AND LEFT$(TOK$, 1) <= "9" THEN
CALL GOTOLINE
END IF
END SUB

SUB INITGETSYM (N AS INTEGER)
CURLINE = N
TEXTP = 1
THELIN$ = PGM$(CURLINE)
CH$ = " "
CALL GETSYM
END SUB

SUB INPUTSTMT
DIM VAR AS INTEGER
IF TOK$ = CHR$(34) THEN
PRINT MID$(TOK$, 2, LEN(TOK$) - 1);
CALL GETSYM
CALL EXPECT(",")
ELSE
PRINT "? ";
END IF
VAR = GETVARINDEX
INPUT VARS(VAR)
END SUB

SUB LISTSTMT
DIM I AS INTEGER
FOR I = 1 TO 1999
IF PGM$(I) <> "" THEN PRINT I; " "; PGM$(I)
NEXT I
PRINT
END SUB

SUB LLISTSTMT
OPEN "LPT1" FOR OUTPUT AS #1
DIM I AS INTEGER
FOR I = 1 TO 1999
IF PGM$(I) <> "" THEN PRINT #1, I; " "; PGM$(I)
NEXT I
PRINT
CLOSE #1
END SUB

SUB LPRINTSTMT
OPEN "LPT1" FOR OUTPUT AS #1
DIM LPRINTNL AS INTEGER
LPRINTNL = 1
DO WHILE TOK$ <> ""
LPRINTNL = 1
IF LEFT$(TOK$, 1) = CHR$(34) THEN
PRINT #1, MID$(TOK$, 2, LEN(TOK$) - 1);
CALL GETSYM
ELSE
PRINT #1, EXPRESSION;
END IF
IF ACCEPT(",") = 0 AND ACCEPT(";") = 0 THEN EXIT DO
PRINTNL = 0
LOOP
IF PRINTNL <> 0 THEN PRINT #1, ""
CLOSE #1
END SUB

SUB PRINTSTMT
DIM PRINTNL AS INTEGER
PRINTNL = 1
DO WHILE TOK$ <> ""
PRINTNL = 1
IF LEFT$(TOK$, 1) = CHR$(34) THEN
PRINT MID$(TOK$, 2, LEN(TOK$) - 1);
CALL GETSYM
ELSE
PRINT EXPRESSION;
END IF


IF ACCEPT(",") = 0 AND ACCEPT(";") = 0 THEN EXIT DO
PRINTNL = 0
LOOP
IF PRINTNL <> 0 THEN PRINT
END SUB

SUB READIDENT
TOK$ = ""
WHILE CH$ >= "A" AND CH$ <= "Z"
TOK$ = TOK$ + CH$
CALL GETCH
WEND
END SUB

SUB READINT
TOK$ = ""
WHILE CH$ >= "0" AND CH$ <= "9"
TOK$ = TOK$ + CH$
CALL GETCH
WEND
NUM = VAL(TOK$)
END SUB

SUB READSTR
TOK$ = CHR$(34)
CALL GETCH
WHILE CH$ <> CHR$(34)
IF CH$ = "" THEN
PRINT "STRING NOT TERMINATED": ERRORS = 1: EXIT SUB
END IF
TOK$ = TOK$ + CH$
CALL GETCH
WEND
CALL GETCH
END SUB

SUB SKIPTOEOL
WHILE CH$ <> ""
CALL GETCH
WEND
CALL GETSYM
END SUB

FUNCTION TERM%
DIM N
N = FACTOR%
TERML:
IF TOK$ = "*" THEN CALL GETSYM: N = N * FACTOR%: GOTO TERML
IF TOK$ = "/" THEN CALL GETSYM: N = N / FACTOR%: GOTO TERML
TERM% = N
END FUNCTION

SUB VALIDLINENUM
IF NUM > 0 AND NUM <= 1999 THEN EXIT SUB
PRINT "LINE NUMBER OUT OF RANGE": ERRORS = 1
END SUB