Page "Literate programming" Paragraph 5

A preprocessor is used to substitute arbitrary hierarchies, or rather " interconnected ' webs ' of macros ", to produce the compilable source code with one command (" tangle "), and documentation with another (" weave ").

The preprocessor also provides an ability to write out the content of the macros and to add to already created macros in any place in the text of the literate program source file, thereby disposing of the need to keep in mind the restrictions imposed by traditional programming languages or to interrupt the flow of thought.