/*
 * parser.cpp
 *
 */

#include <string>
using std::string;

#include "parser.h"

class ParserToken {
private:
	Token	tok;
	bool	pushedBack;

public:
	ParserToken() : pushedBack(false) {}

	Token getToken(istream *in) {
		if( pushedBack ) {
			pushedBack = false;
			return tok;
		}

		return ::getToken(in);
	}
	void pushbackToken(const Token& t) {
		if( pushedBack ) {
			// error
		}
		tok = t;
		pushedBack = true;
	}
} ParserToken;

void
error(const string& msg)
{
	return;
}

ParseTree *
Prog(istream* in)
{
	return StmtList(in);
}

ParseTree *
StmtList(istream* in)
{
	ParseTree *stmt = Stmt(in);
	if( stmt == 0 )
		return 0;

	return new StatementList( stmt, StmtList(in) );
}

ParseTree *	Stmt(istream* in) {
	return 0;
}

ParseTree *	Decl(istream* in) {
	return 0;
}

ParseTree *	Set(istream* in) {
	return 0;
}

ParseTree *	Print(istream* in) {
	return 0;
}

ParseTree *Expr(istream* in) {
	ParseTree *t1 = Term(in);
	if( t1 == 0 )
		return 0;

	for(;;) {
		Token op = ParserToken.getToken(in);
		if( op != T_PLUS && op != T_MINUS ) {
			ParserToken.pushbackToken(op);
			return t1;
		}

		ParseTree *t2 = Expr(in);
		if( t2 == 0 ) {
			error(op.GetLinenum(), "expression required after + or - operator");
			return 0;
		}

		// combine t1 and t2 together
		if( op == T_PLUS )
			t1 = new Addition(op.GetLinenum(), t1, t2);
		else
			t1 = new Subtraction(op.GetLinenum(), t1, t2);
	}

	// should never get here...
	return 0;
}

ParseTree *	Term(istream* in) {
	return 0;
}

ParseTree *	Primary(istream* in) {
	return 0;
}