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#### Parsing

Central to the library is the parser. The parser does the actual work of recognizing a linear input stream of data read sequentially from start to end by the supplied iterators. The parser attempts to match the input following a well-defined set of specifications known as grammar rules. The parser returns a `bool` to report the success or failure. When successful, the parser calls a client-supplied semantic action, if there is one. The semantic action extracts structural information depending on the data passed by the parser and the hierarchical context of the parser it is attached to.

Parsers come in different flavors. The Spirit library comes bundled with an extensive set of pre-defined parsers that perform various parsing tasks from the trivial to the complex. The parser, as a concept, has a public conceptual interface contract. Following the contract, anyone can write a conforming parser that will play along well with the library's predefined components. We shall provide a blueprint detailing the conceptual interface of the parser later.

Clients of the library generally do not need to write their own hand-coded parsers at all. Spirit has an immense repertoire of pre-defined parsers covering all aspects of syntax and semantic analysis. We shall examine this repertoire of parsers in the following sections. In the rare case where a specific functionality is not available, it is extremely easy to write a user-defined parser. The ease in writing a parser entity is the main reason for Spirit's extensibility.

##### The API functions exposed by Spirit.Qi

##### The parse() function

##### The phrase_parse() function

##### The tokenize_and_parse() function

##### The tokenize_and_phrase_parse() function