Node Expression()
{
// Expr := Term {('+' | '-') Term}
Node result = Term();
TokenType token = scanner.Token;
if (token == TokenType.TokenPlus || token == TokenType.TokenMinus)
{
SumNode node = new SumNode(result);
do
{
scanner.Accept();
Node child = Term();
if (token == TokenType.TokenMinus)
{
child = new MultiNode(new NumberNode(new Number(-1)), child);
}
node.Children.Add(child);
token = scanner.Token;
} while (token == TokenType.TokenPlus || token == TokenType.TokenMinus);
result = node;
}
return(result);
}
public override SimplifyResult Replace(out Node node)
{
if (Children.Count == 1)
{
node = Children[0];
return(new SimplifyResult(true));
}
else if (Children.Count == 0)
{
node = new NumberNode(Number.One);
return(new SimplifyResult(true));
}
foreach (Node n in Children)
{
if (typeof(NumberNode).IsInstanceOfType(n) && ((NumberNode)n).Value.N == 0)
{
node = n; // zero
return(new SimplifyResult(true, true));
}
else if (typeof(SumNode).IsInstanceOfType(n))
{
List <Node> l = new List <Node>();
foreach (Node child in ((SumNode)n).Children)
{
List <Node> ll = new List <Node>(Children);
for (int i = 0; i < ll.Count; i++)
{
if (ll[i] == n)
{
ll.RemoveAt(i);
break;
}
}
ll.Add(child);
l.Add(new MultiNode(ll));
}
node = new SumNode(l);
return(new SimplifyResult(true, true));
}
}
node = null;
return(new SimplifyResult(false));
}
