Any parsing expression grammar can be converted directly into a recursive descent parser. V8 first generates an abstract syntax tree with its own parser. The implementations can reuse code from the parser or the compiler for the language. The XML Library provides a simple "pull-style" parser for XML. Lex is commonly used with the yacc parser generator. This idea can be used to generate a recursive descent parser for formulas. The parser and lexical scanner use Bison and Flex. Not every SGML parser can necessarily process every SGML document. The lexical scanner works one symbol ahead of the rest of the parser. However, this grammar can be used by a general CFG parser like the CYK algorithm. The original dissertation gave no algorithm for constructing such a parser given a formal grammar. The first LOLCODE implementation was a PHP parser written by Jeff Jones. They only happen as a result of the parser applying some grammar rule. Interface engine consists of a parser and a test runner. The tokens needed by the Bison parser will be generated using flex.