/// <summary>
/// This is where the work happens
/// </summary>
/// <returns>The symbol that was matched. members _state _line,_column,_position,_buffer and _input are also modified.</returns>
string _Lex()
{
string acc;
var states = _initialStates;
_buffer.Clear();
switch (_state)
{
case -1: // initial
if (!_MoveNextInput())
{
_state = -2;
acc = _GetAcceptingSymbol(states);
if (null != acc)
{
return(acc);
}
else
{
return("#ERROR");
}
}
_state = 0; // running
break;
case -2: // end of stream
return("#EOS");
}
// Here's where we run most of the match. FillMove runs one interation of the NFA state machine.
// We match until we can't match anymore (greedy matching) and then report the symbol of the last
// match we found, or an error ("#ERROR") if we couldn't find one.
while (true)
{
var next = CharFA.FillMove(states, _input.Current);
if (0 == next.Count) // couldn't find any states
{
break;
}
_buffer.Append(_input.Current);
states = next;
if (!_MoveNextInput())
{
// end of stream
_state = -2;
acc = _GetAcceptingSymbol(states);
if (null != acc) // do we accept?
{
return(acc);
}
else
{
return("#ERROR");
}
}
}
acc = _GetAcceptingSymbol(states);
if (null != acc) // do we accept?
{
string be;
if (_blockEnds.TryGetValue(acc, out be) && !string.IsNullOrEmpty(be as string))
{
// we have to resolve our blockends. This is tricky. We break out of the FA
// processing and instead we loop until we match the block end. We have to
// be very careful when we match only partial block ends and we have to
// handle the case where there's no terminating block end.
var more = true;
while (more)
{
while (more)
{
if (_input.Current != be[0])
{
_buffer.Append(_input.Current);
more = _MoveNextInput();
if (!more)
{
return("#ERROR");
}
break;
}
else
{
var i = 0;
var found = true;
while (i < be.Length && _input.Current == be[i])
{
if (!(more = _MoveNextInput()))
{
++i;
found = false;
if (i < be.Length)
{
acc = "#ERROR";
}
break;
}
++i;
}
if (be.Length != i)
{
found = false;
}
if (!found)
{
_buffer.Append(be.Substring(0, i));
}
else
{
more = false;
_buffer.Append(be);
break;
}
if (found)
{
more = _MoveNextInput();
if (!more)
{
break;
}
}
}
}
}
}
return(acc);
}
else
{
// handle the error condition
_buffer.Append(_input.Current);
if (!_MoveNextInput())
{
_state = -2;
}
return("#ERROR");
}
}