private AST GetTerm()
{
//term : factor ((MUL | DIV) factor)*
//------------------------------------------
var node = Factor(); // we start with the first factor
//we can now have 0 or more (MUL | DIV) followed by a new factor
while (currentToken.type == Token.MUL || currentToken.type == Token.DIV)
{
var token = currentToken;
if (currentToken.type == Token.MUL)
{
Eat(Token.MUL); // we found a 'pluss' token, consume it
//result *= Factor(); //add the next term to our result
}
else
{
Eat(Token.DIV);
//result /= Factor();
}
node = new BinOp(node, token, Factor());
}
return(node);
}
private AST Expr()
{
/*
* expr : term ((PLUS | MINUS) term)*
* term : factor ((MUL | DIV) factor)*
* factor : INTEGER | LPAREN expr RPAREN
*/
var node = GetTerm(); //get the starting value
while (currentToken.type == Token.PLUS || currentToken.type == Token.MINUS)
{
var token = currentToken;
if (currentToken.type == Token.PLUS)
{
Eat(Token.PLUS); // we found a 'pluss' token, consume it
}
else
{
Eat(Token.MINUS);
}
node = new BinOp(node, token, GetTerm());
}
return(node);
}
private int VisitBinOp(BinOp node)
{
if (node.op.type == Token.PLUS)
{
var left = Visit(node.left);
var right = Visit(node.right);
return(left + right);
}
if (node.op.type == Token.MINUS)
{
var left = Visit(node.left);
var right = Visit(node.right);
return(left - right);
}
if (node.op.type == Token.MUL)
{
var left = Visit(node.left);
var right = Visit(node.right);
return(left * right);
}
if (node.op.type == Token.DIV)
{
var left = Visit(node.left);
var right = Visit(node.right);
return(left / right);
}
Error();
return(-1);
}