Utilities

This chapter introduces some convenient parsers that we will use when we will be parsing more complex structures.

You are not always interested in what you are parsing. Whitespace is a good example. The skip factory creates a parser that allows you to transform a parser into one that ignores the result.

    #[test]
    fn parse_skip_many_spaces() {
        let input = "           next";
        let parser = skip(many(character(' ')));

        let actual = parser.parse(input);

        let expected = Ok(((), "next"));
        assert_eq!(actual, expected);
    }

An implementation can be given in terms of the primitives and the combinators already given.

space & spaces

A useful building block, to ignore, are white space. The following would be a nice addition to our utility belt. 

    #[test]
    fn parse_spaces() {
        let input = "           \tnext";
        let parser = spaces();

        let actual = parser.parse(input);

        let expected = Ok(((), "next"));
        assert_eq!(actual, expected);
    }

Don't forget about the fact that a tab character also counts as white space.

newline

It is nice to be able to know when a line ends. Line ends are signified by newline. Depending on the that could be one of \n, \r or \r\n.

digit

This parser is an intermediate parser for numbers. It would be nice to be able to parse a digit.

number

Many digits strung together form a number.

end

Sometimes we just want to make sure that we completely parsed a structure. I.e. nothing of the input should be left over after we are finished parsing.

An end parser should come in handy with that. It accepts a parser and depending on that parser succeeds it will either

  • when successful with an empty remainder return the result and an empty remainder.
  • when successful with remaining input report an error.
  • when unsuccessful report the corresponding error.

Exercises

  1. Implement skip parser. Hint: take a look at map
  2. Implement space and spaces parser. Hint: don't forget about skip.
  3. Implement newline. Hint: take a look at one_of.
  4. Implement digit. Hint: take a look at any.
  5. Implement number. Hint: take a look at many and don't forget about digit.
  6. Implement end. Hint closure are parsers as well.