In 1984, Knuth introduced the idea of literate programming and
described a pair of tools to support the practise [#!knuth:84!#].
His approach was to combine Pascal code with TEX documentation to
produce a new language, WEB, that offered programmers a superior
approach to programming. He wrote several programs in WEB,
including weave and tangle, the programs used to support
literate programming.
The idea was that a programmer wrote one document, the web file, that
combined documentation (written in TEX [#!texbook!#]) with code
(written in Pascal).
Running tangle on the web file would produce a complete
Pascal program, ready for compilation by an ordinary Pascal compiler.
The primary function of tangle is to allow the programmer to
present elements of the program in any desired order, regardless of
the restrictions imposed by the programming language. Thus, the
programmer is free to present his program in a top-down fashion,
bottom-up fashion, or whatever seems best in terms of promoting
understanding and maintenance.
Running weave on the web file would produce a TEX file, ready
to be processed by TEX@. The resulting document included a variety of
automatically generated indices and cross-references that made it much
easier to navigate the code. Additionally, all of the code sections
were automatically pretty printed, resulting in a quite impressive
document.
Knuth also wrote the programs for TEX and METAFONT
entirely in WEB, eventually publishing them in book
form [#!tex:program!#,#!metafont:program!#]. These are probably the
largest programs ever published in a readable form.
Inspired by Knuth's example, many people have experimented with
WEB@. Some people have even built web-like tools for their
own favorite combinations of programming language and typesetting
language. For example, CWEB, Knuth's current system of choice,
works with a combination of C (or C++) and TEX [#!levy:90!#].
Another system, FunnelWeb, is independent of any programming language
and only mildly dependent on TEX [#!funnelweb!#]. Inspired by the
versatility of FunnelWeb and by the daunting size of its
documentation, I decided to write my own, very simple, tool for
literate programming.1.1