Editing Lex (software) (section)

==Using Lex with other programming tools==

===Using Lex with parser generators===

Lex, as with other lexical analyzers, limits rules to those which can be described by [[regular expressions]]. Due to this, Lex can be implemented by a [[finite-state automata]] as shown by the [[Chomsky hierarchy]] of languages. To recognize more complex languages, Lex is often used with parser generators such as [[Yacc]] or [[GNU bison|Bison]]. Parser generators use a [[formal grammar]] to parse an input stream.

It is typically preferable to have a parser, one generated by Yacc for instance, accept a stream of tokens (a "token-stream") as input, rather than having to process a stream of characters (a "character-stream") directly. Lex is often used to produce such a token-stream.

[[Scannerless parsing]] refers to parsing the input character-stream directly, without a distinct lexer.

===Lex and make===
[[Make (software)|make]] is a utility that can be used to maintain programs involving Lex. Make assumes that a file that has an extension of <code>.l</code> is a Lex source file. The make internal macro <code>LFLAGS</code> can be used to specify Lex options to be invoked automatically by make.<ref>
{{Cite journal
 |url=http://www.opengroup.org/onlinepubs/009695399/utilities/make.html
 |title=make
 |journal=The Open Group Base Specifications 
 |issue=6
 |publisher=The IEEE and The Open Group
 |year=2004
 |id=IEEE Std 1003.1, 2004 Edition
}}</ref>