Editing Preprocessor (section)

==Lexical preprocessors==
Lexical preprocessors are the lowest-level of preprocessors as they only require [[lexical analysis]], that is, they operate on the source text, prior to any [[parser|parsing]], by performing simple substitution of [[Lexical analysis|tokenized]] character sequences for other tokenized character sequences, according to user-defined rules. They typically perform [[macro substitution]], [[header file|textual inclusion]] of other files, and conditional compilation or inclusion.

===C preprocessor===
{{main|C preprocessor}}
The most common example of this is the [[C preprocessor]], which takes lines beginning with '#' as [[Directive (programming)|directives]].
The C preprocessor does not expect its input to use the syntax of the C language.
Some languages take a different approach and use built-in language features to achieve similar things. For example:
* Instead of macros, some languages use aggressive inlining and templates.
* Instead of includes, some languages use compile-time imports that rely on type information in the object code.
* Some languages use <code>if-then-else</code> and [[dead code elimination]] to achieve [[conditional compilation]].

===Other lexical preprocessors===
Other lexical preprocessors include the general-purpose [[m4 (language)|m4]], most commonly used in cross-platform build systems such as [[autoconf]], and [[general purpose macro processor|GEMA]], an open source macro processor which operates on patterns of context.