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// here this._fa is the target machine we will be parsing.
// parse this or otherwise build it and use it here.
IList<FA> initial = FA.FillEpsilonClosure(this._fa);
IList<FA> next = new List<FA>();
IList<FA> states = new List<FA>(initial);
// start out with an empty capture buffer
this.capture.Clear();
// first move:
if (this.current == -2)
{
    this.Advance();
}
// store the current position
long cursor_pos = this.position;
int line = this.line;
int column = this.column;
while(true) {
    // try to transition from states on
    // the current codepoint under the
    // cursor
    next.Clear();
    FA.FillMove(states, this.current, next);
    if (next.Count > 0)
    {
        // found at least one transition
        // capture the current
        // char, advance the input
        // position:
        this.Advance();
        // move to the next states
        states.Clear();
        FA.FillEpsilonClosure(next, states);
    } else {
        // no matching transition
        // is any current state accepting?
        int acc = FA.GetFirstAcceptSymbol(states);
        if(acc>-1) {
            // accept
            return FAMatch.Create(
                acc,
                this.capture.ToString(),
                cursor_pos,
                line,
                column);
        }
        // not accepting - error
        // keep capturing input until we find a 
        // valid move or there's no more input
        while (this.current != -1 &&
            FA.FillMove(initial, this.current).Count == 0)
        {
            this.Advance();
        }
        if (capture.Length == 0)
        {
            // end of input
            return FAMatch.Create(-2, null, 0, 0, 0);
        }
        // error
        return FAMatch.Create(-1,
            capture.ToString(),
            cursor_pos,
            line,
            column);
 
    }
}