| Home | Libraries | People | FAQ | More

#### Lexer API

###### Description

The library provides a couple of free functions to make using the lexer a snap. These functions have three forms. The first form, `tokenize`, simplifies the usage of a stand alone lexer (without parsing). The second form, `tokenize_and_parse`, combines a lexer step with parsing on the token level (without a skipper). The third, `tokenize_and_phrase_parse`, works on the token level as well, but additionally employs a skip parser. The latter two versions can take in attributes by reference that will hold the parsed values on a successful parse.

###### Header

    // forwards to <boost/spirit/home/lex/tokenize_and_parse.hpp>
    #include <boost/spirit/include/lex_tokenize_and_parse.hpp>

For variadic attributes:

    // forwards to <boost/spirit/home/lex/tokenize_and_parse_attr.hpp>
    #include <boost/spirit/include/lex_tokenize_and_parse_attr.hpp>

The variadic attributes version of the API allows one or more attributes to be passed into the API functions. The functions taking two or more attributes are usable when the parser expression is a Sequence only. In this case each of the attributes passed have to match the corresponding part of the sequence.

Also, see Include Structure.

###### Namespace

Name
`boost::spirit::lex::tokenize`
`boost::spirit::lex::tokenize_and_parse`
`boost::spirit::lex::tokenize_and_phrase_parse`
`boost::spirit::qi::skip_flag::postskip`
`boost::spirit::qi::skip_flag::dont_postskip`

###### Synopsis

The `tokenize` function is one of the main lexer API functions. It simplifies using a lexer to tokenize a given input sequence. It's main purpose is to use the lexer to tokenize all the input.

Both functions take a pair of iterators spanning the underlying input stream to scan, the lexer object (built from the token definitions), and an (optional) functor being called for each of the generated tokens. If no function object `f` is given, the generated tokens will be discarded.

The functions return `true` if the scanning of the input succeeded (the given input sequence has been successfully matched by the given token definitions).

The argument `f` is expected to be a function (callable) object taking a single argument of the token type and returning a bool, indicating whether the tokenization should be canceled. If it returns `false` the function `tokenize` will return `false` as well.

The `initial_state` argument forces lexing to start with the given lexer state. If this is omitted lexing starts in the `"INITIAL"` state.

    template <typename Iterator, typename Lexer>
    inline bool
    tokenize(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , typename Lexer::char_type const* initial_state = 0);

    template <typename Iterator, typename Lexer, typename F>
    inline bool
    tokenize(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , F f
      , typename Lexer::char_type const* initial_state = 0);

The `tokenize_and_parse` function is one of the main lexer API functions. It simplifies using a lexer as the underlying token source while parsing a given input sequence.

The functions take a pair of iterators spanning the underlying input stream to parse, the lexer object (built from the token definitions) and a parser object (built from the parser grammar definition). Additionally they may take the attributes for the parser step.

The function returns `true` if the parsing succeeded (the given input sequence has been successfully matched by the given grammar).

    template <typename Iterator, typename Lexer, typename ParserExpr>
    inline bool
    tokenize_and_parse(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , ParserExpr const& expr)

    template <typename Iterator, typename Lexer, typename ParserExpr
      , typename Attr1, typename Attr2, ..., typename AttrN>
    inline bool
    tokenize_and_parse(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , ParserExpr const& expr
      , Attr1 const& attr1, Attr2 const& attr2, ..., AttrN const& attrN);

The functions `tokenize_and_phrase_parse` take a pair of iterators spanning the underlying input stream to parse, the lexer object (built from the token definitions) and a parser object (built from the parser grammar definition). The additional skipper parameter will be used as the skip parser during the parsing process. Additionally they may take the attributes for the parser step.

The function returns `true` if the parsing succeeded (the given input sequence has been successfully matched by the given grammar).

    template <typename Iterator, typename Lexer, typename ParserExpr
      , typename Skipper>
    inline bool
    tokenize_and_phrase_parse(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , ParserExpr const& expr
      , Skipper const& skipper
      , BOOST_SCOPED_ENUM(skip_flag) post_skip = skip_flag::postskip);

    template <typename Iterator, typename Lexer, typename ParserExpr
      , typename Skipper, typename Attribute>
    inline bool
    tokenize_and_phrase_parse(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , ParserExpr const& expr
      , Skipper const& skipper
      , Attribute& attr);

    template <typename Iterator, typename Lexer, typename ParserExpr
      , typename Skipper, typename Attribute>
    inline bool
    tokenize_and_phrase_parse(
        Iterator& first
      , Iterator last
      , Lexer const& lex
      , ParserExpr const& expr
      , Skipper const& skipper
      , BOOST_SCOPED_ENUM(skip_flag) post_skip, Attribute& attr);

The maximum number of supported arguments is limited by the preprocessor constant `SPIRIT_ARGUMENTS_LIMIT`. This constant defaults to the value defined by the preprocessor constant `PHOENIX_LIMIT` (which in turn defaults to `10`).

| Note
The variadic function with two or more attributes internally combine references to all passed attributes into a `fusion::vector` and forward this as a combined attribute to the corresponding one attribute function.

The `tokenize_and_phrase_parse` functions not taking an explicit `skip_flag` as one of their arguments invoke the passed skipper after a successful match of the parser expression. This can be inhibited by using the other versions of that function while passing `skip_flag::dont_postskip` to the corresponding argument.

###### Template parameters

Parameter | Description
--- | ---
`Iterator` | `ForwardIterator` pointing to the underlying input sequence to parse.
`Lexer` | A lexer (token definition) object.
`F` | A function object called for each generated token.
`ParserExpr` | An expression that can be converted to a Qi parser.
`Skipper` | Parser used to skip white spaces.
`Attr1`, `Attr2`, ..., `AttrN` | One or more attributes.