********       A Very Simple  COMPILER MANUAL      ********
	********       by Louis Guzik  April 29, 1995	   ********

	********       Call if you have any questions      ********
				341-2606



Max Chars per Line is 40 chars.




MY STATIC MEMORY
		----------------------------
		|  0 - 9   : 10 CONSTANTS  |
		|--------------------------|
		| 10 - 35  : 26 VARS       |
		|--------------------------|
		| 36       : START of CODE |
		|--------------------------|
		| MEM_END  : END of MEM    |
		----------------------------




Machine Code	OpCode	Operand 		Comment
----------------------------------------------------------------------------
	1	Load	Var | Const	; Load Accumulator with address
	2	Store	Var		; Store from Accum. to Address
	3	Read	---		; Read from Keyboard to Accum
	4	Write	---		; Write Addr in Accum to CRT Screen
	5	Print	Str		; Print Addr of Str in Accum to CRT Screen
	6	Cmp	Var		; Compare Var to Accum, if Accum == Var do stmt.
	7	Not	Var		; Compare Var to Accum, if Accum != Var do stmt.
	8	Add	Var		; Add; Accum = Accum + Var
	9	Sub	Var		; Subtract; Accum = Accum - Var
	10	Mul	Var		: Multiply; Accum = Accum * VAr
	11	Div	Var		; Divide; Accum = Accum / Var
	12	Jmp	Label		; Jump to a label
	13	Halt	---		; End of program




LANG. RULES
	1	S --> ASSIGN id = A;
	2	S --> COMPUTE id = A oper A;
	3	S --> WRITE id | string;
	4	S --> READ id;
	5	S --> S*
	6	S --> IF A = A  S_Special;
	7	A --> id | constant;
	8	S_Special --> ASSIGN id = A; | WRITE id | string; | READ id;


	id:		a single alpha character, A to Z.
	string:		" any string of chars "  or  "\n".
	constant:	intergers values between 0 and 9.
	operators:	+ add, - subtract, * multiply, / divide, = equal, ! not equal.



EXAMPLE PROGRAM
	write "Enter x ==>";
	read x;
	write "x = ";
	write x;
	write "\n";

	if x = 0  write "Enter New x =>";
	if x = 0  read x;
	if x ! 0  assign b = x;

	write "x = ";
	write x;
	write "\n";

	write "b=x c=9 d=c/b d=";
	assign c = 9;
	compute d = c / b;
	write d;







 - To start the compiler, run the program "COMPILER".

 - DeBug mode shows in table form, what the compiler is doing.

 - Default source input file name is SOURCE.VSL, you may enter a new name.

 - The program has five (5) parts: MAIN, LEX, PARSER, GEN_CODE and EXECUTE.

 - MAIN is very small and calls the other parts.

 - LEX; works as a State Machine.  Based on in class diagram from teacher.

 - RECURSIVE DESCENT PARSER;  Based on Compiler Design textbook Ch. 4 page 102.

 - GEN_CODE; based on handout from teacher, generates machine code.

 - EXECUTE; my own design, executes machine code





*******   END OF MANUAL.