public string visit(BinOp node)
{
switch (node.op.type)
{
case tokens.PLUS:
return(Convert.ToString(Convert.ToInt32(node.left.accept(this)) + Convert.ToInt32(node.right.accept(this))));
case tokens.MINUS:
return(Convert.ToString(Convert.ToInt32(node.left.accept(this)) + Convert.ToInt32(node.right.accept(this))));
case tokens.MUL:
return(Convert.ToString(Convert.ToInt32(node.left.accept(this)) * Convert.ToInt32(node.right.accept(this))));
case tokens.DIV:
return(Convert.ToString(Convert.ToInt32(node.left.accept(this)) / Convert.ToInt32(node.right.accept(this))));
}
return(visit(node));
}
// term: factor ((MUL|DIV) factor)*
public AST term()
{
AST node = factor();
string[] valid_operators = new string[] { tokens.MUL, tokens.DIV };
while (Array.IndexOf(valid_operators, current_token.type) != -1)
{
Token t = current_token;
if (t.type == tokens.MUL)
{
eat(tokens.MUL);
}
else if (t.type == tokens.DIV)
{
eat(tokens.DIV);
}
node = new BinOp(node, t, factor());
}
return(node);
}
// expr: term ((PLUS|MINUS) term)*
public AST expr()
{
AST node = term();
/* ((PLUS|MINUS) term)* turns into a while loop */
string[] valid_operators = new string[] { tokens.PLUS, tokens.MINUS };
while (Array.IndexOf(valid_operators, current_token.type) != -1)
{
Token t = current_token;
if (t.type == tokens.PLUS)
{
eat(tokens.PLUS);
}
else if (t.type == tokens.MINUS)
{
eat(tokens.MINUS);
}
node = new BinOp(node, t, term());
}
return(node);
}
