/*
 * This is the basic expression grammar for four function
 * Expressions. The grammar support the plus (+), minus (-)
 * multiply (*), and divide (/) operations.
 *
 * See Calc1i.jack for a grammar that parses and implements
 * the functions.
 *
 * Example grammar written 11/1/96 by Chuck McManis (cmcmanis@netcom.com)
 */

options {
LOOKAHEAD=1;
}

PARSER_BEGIN(Calc1)

public class Calc1 {

    public static void main(String args[]) throws ParseError {
	Calc1 parser = new Calc1(System.in);
	while (true) {
	    System.out.print("Enter Expression: ");
	    System.out.flush();
	    try {
		switch (parser.one_line()) {
		    case -1:
			System.exit(0);
		    default:
			break;
		}
	    } catch (ParseError x) {
		System.out.println("Exiting.");
		throw x;
	    }
	}
    }
}
PARSER_END(Calc1)

IGNORE_IN_BNF :
{}
{
 	" "
|	"\r"
|	"\t"
}



TOKEN :
{ }
{
	< EOL: "\n" >
}

TOKEN : /* OPERATORS */
{ }
{
	< PLUS: "+" >
|	< MINUS: "-" >
|	< MULTIPLY: "*" >
|	< DIVIDE: "/" >
}

TOKEN :
{ }
{
    < CONSTANT: ( <DIGIT> )+ >
|   < #DIGIT: ["0" - "9"] >
}

int one_line() :
{}
{
    sum() <EOL>
	{ return 1; }
  | <EOL>
	{ return 0; }
  | <EOF>
	{ return -1; }
}

void sum() :
{ }
{
    term() (( <PLUS> | <MINUS> ) term())*
}

void term() :
{ }
{
    unary() (( <MULTIPLY> | <DIVIDE> ) unary())*
}

void unary() :
{ }
{
    <MINUS> element()
  |     element()
}

void element() :
{}
{
    <CONSTANT>
|   "(" sum() ")"
}