APT Parser

##Grammar In BNF:

Stmt ::= Assign | While | Print
Assign ::= ID = Expr ;
Expr ::= INT + Expr | INT - Expr | INT < Expr | INT > Expr | INT
While ::= WHILE Expr { stmt* }
Print ::= PRINT Expr ;

##Parser Usage Make sure to import the expression classes:

import expressions.*;

Load your source code in to a String (for example, using a FileReader and StringBuilder), then invoke the parser as follows:

ArrayList<AbstractExpression> p = Parser.parse(s);

If the parser ran without any errors, the ArrayList p will now contain a parsed set of expressions from your source code. ##Expressions All expressions implement the interface AbstractExpression; which has one method String pp() returning the respective source code for that expression. Each expression also has a getter for each of its attributes. ###List of expressions

Expression class	Name	Example	Attributes
Variable	Variable	i	name
Int	Integer	42	val
Assignment	Assignment	i = 5 or i = j + 5	name,exp
BinaryOP	Binary Operation	i < 5	lhs,op,rhs
WhileLoop	While loop	while i < 100 { i++ }	cond,body
Print	Print out	print i	exp

##Example implementation ####ParserTester.java

import expressions.AbstractExpression;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;

public class ParserTester {

    public static void main(String[] args) {
        String s = null;
        //read file > s
        try {
            BufferedReader br = new BufferedReader(new FileReader(args[0]));
            StringBuilder sb = new StringBuilder();
            String line = br.readLine();

            while (line != null) {
                sb.append(line);
                sb.append("\n");
                line = br.readLine();
                s = sb.toString();
            }
        } catch (FileNotFoundException e) {
            System.out.println("File not found!");
            System.exit(1);
        } catch (IOException e) {
            System.out.println("IO Exception!");
            System.exit(1);
        }
        //parse
        ArrayList<AbstractExpression> p = Parser.parse(s);
        //test
        System.out.printf("We parsed %d expressions:\n", p.size());
        for (AbstractExpression e : p) {
            System.out.println(e.pp() + "\n--");
        }
    }
}

Running java ParserTester.java p1.hll will produce the following output:

We parsed 3 expressions:
i = 0 + 2;
--
j = i + 1;
--
while i < 100{
  i = i - 1;
  j = j + 1 + 2;
  print i;
}
--