private TreeNode ParseOr()
{
var head = ParseCat();
while (PeekAndDiscard('|'))
{
var tail = ParseCat();
head = new TreeNode
{
Type = NodeType.Or,
Left = head,
Right = tail,
};
}
return head;
}
public TreeNode Parse()
{
var head = ParseOr();
if (PeekAndDiscard(']'))
{
Expect('[');
var tail = ParseOr();
head = new TreeNode
{
Type = NodeType.Cut,
Left = head,
Right = tail
};
}
return head;
}
private TreeNode ParseCat()
{
var prev = ParseFactor();
for (; ; )
{
var tail = ParseFactor();
if (tail == null)
break;
var node = new TreeNode
{
Type = NodeType.Cat,
Left = prev,
Right = tail
};
prev = node;
}
return prev;
}
