Python front-end for Noweb literate tool

The idea behind literate programming, that a program can be a piece of literature, is due to Donald E. Knuth. Knuth is an extremely respected figure in programming community (and also among combinatorics and computer science people). In this paradigm, one does not write a program based on how computer would reason about it but rather follows a human like flow. It is the job of literate programming tool to convert this human-readable program into something which make sense to a computer. There is much freedom for a programmer to write his code the way he likes it but since the translation process is governed by a computer program, there are specific constraints on how to write a program in literate way.

Best way to understand the difference between a normally commented and literate program is to have a look at a literate program. One can easily find many on Knuth’s home page. A program is written like an essay, and one then uses a tool to extract code (this process was called tangling by Knuth) or documentation (process called weaving) out of it. Knuth, true to his nature, wrote cweb for his personal use. Some other tools cropped up on these lines and many of them were written for pacific languages. Noweb, written by Roman Ramsay, is language agnostic. There are some other tools like it e.g. funnel-web, nuweb etc but none is as simple to use as this one. Lyx also have support for noweb. And if my memory serves me write, IIT Madras, offered (or still offering) a course in literate programming to its students using Lyx.

Literate programming did not really catch up (who wants to write documentation in the first place). But some people have used it extensively. To my knowledge, apart from Knuth, Columbia Esterel Compiler (cec) is written as literate program using noweb and its really easy to understand (well, not really but relatively). I was able to make changes to it for my personal fun.

A python front-end for noweb

Script is here

I found one thing lacking in noweb that I have to write full program in one file or use makefiles to automate the process. This is OK but I was not happy. I wrote a python script to do the following,

  • There is one main file which include other files using %\include{file.nw} macro. Notice that this approach is like tex. Our macro will be treated as comment by normal tex program but not by this python front-end.
  • Write as many noweb files as you like and using %\include macro to include other literate files.
  • Pass the main file to python script with optional command (tangling or weaving)
  • You can attach a line over chunk name to tell this script that you want to write this chunk to some specific file. Write over the chunk something like %file:src/file.c. For example, if a chunk named gloabal.h is to be written to file include/global.h then, just above the chunk <<global.h>>, you must have
   %file:include/global.h
   <>=
   // whatver is there in global
   @ %def global.h 

Download the script and run it without any argument to see the possible commands. Report an issue on its github repo if you locate a bug.

 

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