;THE IL CONTROL SECTION 

START:  INIT                  ;INITIALIZE 
        NLINE                 ;WRITE CRLF 
CO:     GETLINE               ;WRITE PROMPT AND GET LINE 
        TSTL    XEC           ;TEST FOR LINE NUMBER 
        INSERT                ;INSERT IT (MAY BE DELETE) 
        JMP     CO 
XEC:    XINIT                 ;INITIALIZE 

;STATEMENT EXECUTOR 

STMT:   TST     S1,'LET'      ;IS STATEMENT A LET 
        TSTV    S17           ;YES, PLACE VAR ADDRESS ON AESTK 
        TST     S17,'='       ;(This line originally omitted) 
        CALL    EXPR          ;PLACE EXPR VALUE ON AESTK 
        DONE                  ;REPORT ERROR IF NOT NEXT 
        STORE                 ;STORE RESULT 
        NXT                   ;AND SEQUENCE TO NEXT 
S1:     TST     S3,'GO'       ;GOTO OT GOSUB? 
        TST     S2,'TO'       ;YES...TO, OR...SUB 
        CALL    EXPR          ;GET LABEL 
        DONE                  ;ERROR IF CR NOT NEXT 
        XPER                  ;SET UP AND JUMP 
S2:     TST     S17,'SUB'     ;ERROR IF NO MATCH 
        CALL    EXPR          ;GET DESTINATION 
        DONE                  ;ERROR IF CR NOT NEXT 
        SAV                   ;SAVE RETURN LINE 
        XPER                  ;AND JUMP 
S3:     TST     S8,'PRINT'    ;PRINT 
S4:     TST     S7,'"'        ;TEST FOR QUOTE 
        PRS                   ;PRINT STRING 
S5:     TST     S6,','        ;IS THERE MORE? 
        SPC                   ;SPACE TO NEXT ZONE 
        JMP     S4            ;YES JUMP BACK 
S6:     DONE                  ;ERROR IF CR NOT NEXT 
        NLINE 
        NXT 
S7:     CALL    EXPR 
        PRN                   ;PRINT IT 
        JMP     S5            ;IS THERE MORE? 
S8:     TST     S9,'IF'       ;IF STATEMENT 
        CALL    EXPR          ;GET EXPRESSION 
        CALL    RELOP         ;DETERMINE OPR AND PUT ON STK 
        CALL    EXPR          ;GET EXPRESSION 
        TST     S17,'THEN'    ;(This line originally omitted) 
        CMPR                  ;PERFORM COMPARISON -- PERFORMS NXT IF FALSE 
        JMP     STMT 
S9:     TST     S12,'INPUT'   ;INPUT STATEMENT 
S10:    CALL    VAR           ;GET VAR ADDRESS 
        INNUM                 ;MOVE NUMBER FROM TTY TO AESTK 
        STORE                 ;STORE IT 
        TST     S11,','       ;IS THERE MORE? 
        JMP     S10           ;YES 
S11:    DONE                  ;MUST BE CR 
        NXT                   ;SEQUENCE TO NEXT 
S12:    TST     S13,'RETURN'  ;RETURN STATEMENT 
        DONE                  ;MUST BE CR 
        RSTR                  ;RESTORE LINE NUMBER OF CALL 
        NXT                   ;SEQUENCE TO NEXT STATEMENT 
S13:    TST     S14,'END' 
        FIN 
S14:    TST     S15,'LIST'    ;LIST COMMAND 
        DONE 
        LST 
        NXT 
S15:    TST     S16,'RUN'     ;RUN COMMAND 
        DONE 
        NXT 
S16:    TST     S17,'CLEAR'   ;CLEAR COMMAND 
        DONE 
        JMP     START 

S17:    ERR                   ;SYNTAX ERROR 

EXPR:   TST     E0,'-' 
        CALL    TERM          ;TEST FOR UNARY -. 
        NEG                   ;GET VALUE 
        JMP     E1            ;NEGATE IT 
E0:     TST     E1A,'+'       ;LOOK FOR MORE 
E1A:    CALL    TERM          ;TEST FOR UNARY + 
E1:     TST     E2,'+'        ;LEADING TERM 
        CALL    TERM 
        ADD 
        JMP     E1 
E2:     TST     E3,'-'        ;ANY MORE? 
        CALL    TERM          ;DIFFERENCE TERM 
        SUB 
        JMP     E1 
E3:T2:  RTN                   ;ANY MORE? 
TERM:   CALL    FACT 
TO:     TST     T1,"*"
        CALL    FACT          ;PRODUCT FACTOR. 
        MPY 
        JMP     T0 
T1:     TST     T2,'/' 
        CALL    FACT          ;QUOTIENT FACTOR. 
        DIV 
        JMP     T0 

FACT:   TSTV    F0 
        IND                   ;YES, GET THE VALUE. 
        RTN 
F0:     TSTN    F1            ;NUMBER, GET ITS VALUE. 
        RTN 
F1:     TST     F2,'('        ;PARENTHESIZED EXPR. 
        CALL    EXPR 
        TST     F2,')' 
        RTN 
F2:     ERR                   ;ERROR. 

RELOP:  TST     RO,'=' 
        LIT     0             ;= 
        RTN 
R0:     TST     R4,'<' 
        TST     R1,'=' 
        LIT     2             ;<= 
        RTN 
R1:     TST     R3,'>' 
        LIT     3             ;<> 
        RTN 
R3:     LIT     1             ;< 
        RTN 
R4:     TST     S17,'>' 
        TST     R5,'=' 
        LIT     5             ;>= 
        RTN 
R5:     TST     R6,'<' 
        LIT     3 
        RTN                   ;(This line originally omitted) 
R6:     LIT     4 
        RTN