PL-0-Compiler

Compile in Eustis:
In the same directory (needed):
	lex.c
	parser.c
	codegen.c
	vm.c
	hw4compiler.c
	headers.h
	<filename>.txt
	
To run the compiler, use the following in command line of Eustis:

	gcc -o compile lex.c vm.c parser.c codegen.c compiler.c
	./compile <filename>.txt <-l> <-a> <-v>

Input/Output: 
	Lexical Analyzer - <filename>.txt
		   Contains source code written in PL/0 programming language
		   
		   lexAnayzerOutput.txt 
		   Contains: Source Program, Lexeme Table, Lexeme List
			
		   tokens.txt
		   Contains: Lexeme List	

Parser - tokens.txt
	 Output from Lexical Analyzer
	    
	 parserOutput.txt
         Contains: Generated errors if any; otherwise no errors, program is syntactically correct!
	      		 
Codegen - tokens.txt
	  Output from Lexical Analyzer
	
              ICGOutput.txt
          Contains: Assembly Code to be used in vm

Vitual Machine - ICGOutput.txt
		 Output from Codegen
		
		 vmOutput.txt
		 Contains: Program in interpreted assembly language with line numbers
                               The execution of program in the virtual machine, showing the stack, pc, bp, and sp
Purpose:
	Implementing compiler for tiny PL/O machine
	--> Lexical Anayzer 
	--> Recursice Descent Parser
	--> Intermediate Code Generator
	--> Virtual Machine
	--> Compiler Driver

Lexical Analyzer:
	--> Capable to read in a source program written in PL/0
	--> Identify some errors; variable number does not start with a letter, number/name too long, and invalid symbols
	--> Produce, as output, the source program, the source program lexeme table, and a list of lexemes

Recursive Descent Parser:
	--> Read inputs from Scanner (HW2) and parses the lexemes
	--> Symbol Table is created
	--> Outputs generated error messages if not syntactically correct

Intermediate Code Generator:
	--> If error is not generated by the Parser, then the execution of the compiler driver continues with icg  
	--> Generates the assembly language <op, l, m> using tokens from Scanners (HW2)     
	--> Outputs assembly language for Virtual Machine (HW1)

Virtual Machine:
	--> Stack Machine with two memory stores; stack and data area
	--> The Insturction Set Architectur with 23 instructions
	--> Requires two steps Fetch&Execute
	--> Outputs interpreted assembly language and execution of program showing the stack, pc, bp, and sp

Compiler Driver & Directives: 
	Combine all of the compiler parts into one single program.
	--> -l Lexical Analyzer Output
	--> -a Parser/Codegen Output 
	--> -v Virtual Machine Output