docs: public static Token instanceFor(final char c)
      {
          if (c == '\'' || c == '"')
              return new TokLiteral(c);
  
          if (Character.isDigit(c) || c == '-' || c == '.')
              return new TokNumber();
  
          if (Character.isLetter(c) || c == '_')
              return new TokVariable();
  
          return new TokOperator();
      }