Compared to NoWeb, Anansi’s primary benefits are the ability to include separate files, and to automatically generate an entire directory tree from a project without having to enumerate each output.
Literate programming is a programming paradigm introduced by Donald Knuth in which a program is given as an explanation of the program logic in a natural language, such as English, interspersed with snippets of macros and traditional source code, from which a compilable source code can be generated.
I learned about literate programming from Literate Haskell, an official syntactic extension for the Haskell language that allows code and commentary to be easily combined in the same file. The language spec provides examples of Haskell code embedded within LaTeX. I was fresh out of university at the time and hadn't learned how to organize non-trivial codebases yet, so having a clear example derived from the experience of Donald Knuth was attractive.
To learn more, I decided to write a D-Bus
Next I decided to get closer to the origins of Literate Programming, and use NoWeb. NoWeb is very similar to the original CWEB in behavior, and among other interesting design choices it receives the entire document input as a single source file. After a few abandoned attempts to generate this file from smaller fragments, version 0.5 of my library was released as two giant NoWeb documents: dbus-core.nw and Tests.nw.
I used NoWeb for roughly 8 months for haskell-dbus, experimenting with various ways of structuring the document and processing the LaTeX markup into a human-readable document. Eventually the pain of working within a single massive source file became overwhelming, and I decided to write my own literate programming tool that could consume a filesystem hierarchy. This was the first version of Anansi.
I continued to use and develop Anansi for a few years. It actually got pretty good output – see dbus-core_0.9.2.1.pdf for 102 pages of typeset D-Bus client library implementation.
But in the end, I was never able to realize the promised benefits of Literate Programming. The typeset PDF was not easier to read than hypertext documentation generated by Haddock, and both were obviously worse than the very nice docs being created by the Python community with Sphinx.
So in mid 2012 (~3 years after starting the project) I removed all the literate annotations and styles, dropped the fancy build scripts, and released haskell-dbus 0.10 as standard Haskell.
I also stopped working on Anansi at that time. It does work, it'll do exactly what it says on the tin and process your literate source files to separate the content from the commentary. I'm just not not convinced any more this is a useful goal.
Anansi has eight commands:
:includewill behave as if the contents of the file at the given path is inserted at the current position. This is useful for separating a large project into more manageable segments. Paths are resolved relative to the current file.
tab-size, which controls how many spaces a single tab is expanded to in LaTeX output.
:into the output.
To generate haskell code from an Anansi file, run anansi tangle -o "output path". To generate literate markup, run anansi weave -o "output path".
:loom anansi-hscolour.html :option tab-size=8 <!DOCTYPE html> <html> <head><title>anansi example</title></head> <body> <p>This is an example of using Anansi to generate an HTML document and Haskell code from the same source.</p> :d main main :: IO () main = do putStrLn "Here we are in our cool main function!" : <p>Lets pull in some imports, to demonstrate how literate programming enables out‐of‐order document construction:</p> :d imports import System.Environment (getProgName) : :d main progName <- getProgName putStrLn ("This program was run as " ++ progName) : <p>And we'll write the whole thing out to a single file, <tt>Main.hs</tt>:</p> :f Main.hs |imports| |main| : </body> </html>
which is rendered to:
and generates a single Haskell file, `Main.hs`:
import System.Environment (getProgName) main :: IO () main = do putStrLn "Here we are in our cool main function!" progName <- getProgName putStrLn ("This program was run as " ++ progName)
While the basic looms available will work for some documents, many users will want to write their own looms to generate specialized markup. For example, one might want to use an existing LaTeX style for an academic paper, or Markdown for posting to a forum. Custom looms allow complete customization of the weaving process.
See the API documentation, and perhaps the source code to Anansi's built-in looms (such as
Pandoc is a general-purpose markup converter. It can take pretty much any kind of text document and convert it into a different format. The
anansi-pandoc library provides Anansi looms backed by Pandoc.
Code: https://john-millikin.com/code/anansi-pandoc (GitHub mirror).
HsColour is a library for syntax highlighting of Haskell code. At the time it was the best option for generating nice colorful output. In modern codebases, you should use one of the many unified syntax highlighting libraries such as Pygments, src-highlite, HighlightJS, or Chroma.
Code: https://john-millikin.com/code/anansi-hscolour (GitHub mirror).
D-Bus is the inter-process communication protocol used by most Free Software desktop platforms, most notably Linux.