public ExpNode parseExp()
{
OpExpNode exp = null;
ExpNode fact = null;
if (lex.Peek() == Token.SUB)
{
exp = new OpExpNode();
exp.left = null;
exp.OP = lex.Take();
exp.right = parseFact();
}
else
{
fact = parseFact();
}
while (lex.Peek() == Token.ADD || lex.Peek() == Token.SUB)
{
OpExpNode tmp = new OpExpNode();
tmp.left = exp == null ? fact : exp;
tmp.OP = lex.Take();
tmp.right = parseFact();
exp = tmp;
}
return(exp == null ? fact : exp);
}
private ExpNode parseExpnt()
{
ExpNode elm = parseElmnt();
if (lex.Peek() != Token.POW)
{
return(elm);
}
OpExpNode exp = new OpExpNode();
exp.left = elm;
exp.OP = lex.Take();
exp.right = parseExpnt();
return(exp);
}
private ExpNode parseFact()
{
ExpNode expn = parseExpnt();
OpExpNode exp = null;
while (lex.Peek() == Token.MUL || lex.Peek() == Token.DIV)
{
OpExpNode tmp = new OpExpNode();
tmp.left = exp == null ? expn : exp;
tmp.OP = lex.Take();
tmp.right = parseExpnt();
exp = tmp;
}
return(exp == null ? expn : exp);
}
