Literate Programming - Tools

Tools

The first published literate programming environment was WEB, introduced by Donald Knuth in 1981 for his TeX typesetting system; it uses Pascal as its underlying programming language and TeX for typesetting of the documentation. The complete commented TeX source code was published in Knuth's TeX: The program, volume B of his 5-volume Computers and Typesetting. Knuth had privately used a literate programming system called DOC as early as 1979. He was inspired by the ideas of Pierre-Arnoul de Marneffe. The free CWEB, written by Knuth and Silvio Levy, is WEB adapted for C and C++, runs on most operating systems and can produce TeX and PDF documentation.

There are various other implementations of the literate programming concept:

• noweb is independent of the programming language of the source code. It is well known for its simplicity: just two text markup conventions and two tool invocations are needed to use it, and it allows for text formatting in HTML rather than going through the TeX system.

• FunnelWeb is another LP tool that can produce HTML documentation output. It has more complicated markup (with "@" escaping any FunnelWeb command), but has many more flexible options (see). Like noweb, it is independent of the programming language of the source code.

• Nuweb can translate a single LP source into any number of code files in any mix of languages together with documentation in LaTeX. It does it in a single invocation; it does not have separate weave and tangle commands. It does not have the extensibility of noweb, but it can use the listings package of LaTeX to provide pretty-printing and the hyperref package to provide hyperlinks in PDF output. It also has extensive indexing and cross-referencing facilities including cross-references from the generated code back to the documentation, both as automatically generated comments and as strings that the code can use to report its behaviour. Vimes is a type-checker for Z notation which shows the use of nuweb in a practical application. Around 15,000 lines of nuweb source are translated into nearly 15,000 lines of C/C++ code and over 460 pages of documentation. See External links.

• Molly is a LP tool written in Perl, which aims to modernize and scale it with "folding HTML" and "virtual views" on code. It uses "noweb" markup for the literate source files. See External links.

• Codnar is an inverse literate programming tool available as a Ruby Gem (see External links). Instead of the machine-readable source code being extracted out of the literate documentation sources, the literate documentation is extracted out of the normal machine-readable source code files. This allows these source code files to be edited and maintained as usual. The approach is similar to that used by popular API documentation tools, such as JavaDoc. Such tools, however, generate API reference documentation, while Codnar generates a linear narrative describing the code, similar to that created by classical LP tools. Codnar can co-exist with API documentation tools, allowing both a reference manual and a linear narrative to be generated from the same set of source code files.

• The Leo text editor is an outlining editor which supports optional noweb and CWEB markup. The author of Leo mixes two different approaches: first, Leo is an outlining editor, which helps with management of large texts; second, Leo incorporates some of the ideas of literate programming, which in its pure form (i.e. the way it is used by Knuth Web tool and/or tools like "noweb") is possible only with some degree of inventiveness and the use of the editor in a way not exactly envisioned by its author (in modified @root nodes). However, this and other extensions (@file nodes) make outline programming and text management successful and easy and in some ways similar to literate programming.

• The Haskell programming language has native support for semi-literate programming, inspired by CWEB but with a simpler implementation. When aiming for TeX output, one writes a plain LaTeX file where source code is marked by a given surrounding environment; LaTeX can be set up to handle that environment, while the Haskell compiler looks for the right markers to identify Haskell statements to compile, removing the TeX documentation as if they were comments. However, as described above, this is not literate programming in the sense intended by Knuth. Haskell's functional, modular nature makes literate programming directly in the language somewhat easier, but it is not nearly as powerful as one of the WEB tools where "tangle" can reorganize in arbitrary ways.

• The Web 68 Literate Programming system uses Algol 68 as the underlying programming language, although there is nothing in the pre-processor 'tang' to force the use of that language.