Re-Establish Skipping (skip[])

Re-Establish Skipping (`skip[]`)

Description

The skip directive is the inverse of lexeme. While the lexeme directive turns off white space skipping, the skip directive turns it on again. This is simply done by wrapping the parts inside the skip directive:

skip[a]

It is also possible to supply a skip parser to the skip directive:

skip(p)[a] // Use `p` as a skipper for parsing `a`

This makes it possible to:

Perform localized phrase level parsing while doing character level parsing.
Replace the current skipper anywhere with an entirely different skipper while doing phrase level parsing.

Header

// forwards to <boost/spirit/home/qi/directive/skip.hpp>
#include <boost/spirit/include/qi_skip.hpp>

Also, see Include Structure.

Namespace

Name
`boost::spirit::skip // alias: boost::spirit::qi::skip`

Model of

UnaryParser

Notation

a: A Parser.

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in UnaryParser.

Expression	Semantics
`skip[a]`	Re-establish the skipper that got inhibited by lexeme
`skip(p)[a]`	Use `p` as a skipper for parsing `a`

Attributes

See Compound Attribute Notation.

Expression	Attribute
`skip[a]`	a: A --> skip[a]: A a: Unused --> lexeme[a]: Unused
`skip(p)[a]`	a: A --> skip(p)[a]: A a: Unused --> lexeme[a]: Unused

Expression

Attribute

skip[a]

a: A --> skip[a]: A
a: Unused --> lexeme[a]: Unused

skip(p)[a]

a: A --> skip(p)[a]: A
a: Unused --> lexeme[a]: Unused

Complexity

The complexity is defined by the complexity of the subject parser, a

Example

	Note
	The test harness for the example(s) below is presented in the Basics Examples section.

Some using declarations:

using boost::spirit::qi::skip;
using boost::spirit::qi::int_;
using boost::spirit::ascii::space;

Simple usage of skip[]:

Explicitly specify a skip parser. This parser parses comma delimited numbers, ignoring spaces.

test_parser("1, 2, 3, 4, 5", skip(space)[int_ >> *(',' >> int_)]);