private letter Parse_letter()
{
if (_index >= _tokens.Count())
{
return(null);
} // must be first line on any atom
/* letter:
* "A-Za-z" */
var _data = _tokens[_index];
var _result = new letter(_data);
if (_result.is_letter)
{
_index++;
return(_result);
}
else
{
return(null);
}
}
public letter_sequence(letter _letter, letter_sequence _letter_sequence)
{
letter = _letter;
self_letter_sequence = _letter_sequence;
expression = self_letter_sequence?.expression + letter.expression;
}
public letter_sequence(letter _letter)
{
letter = _letter;
expression = letter.expression;
}