public LLkParser(TableGenerator tg, IEnumerable <Token> input)
{
_tg = tg;
_input = input.GetEnumerator();
_stack = new Stack <_Entry>();
_nodeType = LLNodeType.Initial;
_current = new List <Token>();
}
public bool Read()
{
var n = NodeType;
if (LLNodeType.Error == n && 0 == _current.Count)
{
_errorToken.Symbol = null;
_stack.Clear();
return(true);
}
if (LLNodeType.Initial == n)
{
_stack.Push(new _Entry(0)); // start at T0
var kk = 0;
// read k tokens from the input
while (_input.MoveNext() && kk < _tg.k)
{
_current.Add(_input.Current);
++kk;
}
return(true);
}
// clear the error status
_errorToken.Symbol = null;
if (0 < _stack.Count)
{
var entry = _stack.Peek();
var sid = _stack.Peek();
if (entry.IsEndSymbol)
{
_nodeType = LLNodeType.EndNonTerminal;
_stack.Pop();
return(true);
}
if (entry.Symbol == _input.Current.Symbol) // terminal
{
// lex the next token
_input.MoveNext();
_stack.Pop();
return(true);
}
// non-terminal
Dictionary <string, CfgRule> d;
if (_parseTable.TryGetValue(sid, out d))
{
CfgRule rule;
if (d.TryGetValue(_input.Current.Symbol, out rule))
{
_stack.Pop();
// store the end non-terminal marker for later
_stack.Push(string.Concat("#END ", sid));
// push the rule's derivation onto the stack in reverse order
var ic = rule.Right.Count;
for (var i = ic - 1; 0 <= i; --i)
{
sid = rule.Right[i];
_stack.Push(sid);
}
return(true);
}
_Panic();
return(true);
}
_Panic();
return(true);
}
// last symbol must be the end of the input stream or there's a problem
if ("#EOS" != _input.Current.Symbol)
{
_Panic();
return(true);
}
return(false);
}
