Explanation and Motivation

We continue our reading of Literate Programming, by Donald Knuth.

In this session, we completed up to the end of section 5. Knuth has by now given the ‘plan’ of his program to print the first m prime numbers, and has commenced his explanation of the program’s ‘output phase’.

Our discussion focussed on the link between ‘motivation’ and explanation in Knuth’s vision for WEB. Knuth essentially argues that the prose of a WEB program ought to ‘motivate’ the programming decisions expressed in the code. His model for this process is the essay, which he perceives as a literary form in which the writer records their own thought-process. The source of a WEB program thus ought to reflect the programmer’s own creative process.

This is a powerful model of composition. From a literary studies perspective, it recalls the approach of the late Helen Vendler, who famously interpreted poems as records of their own creative process.

But many in the group objected to aspects of Knuth’s argument.

In the first case, does an essay ever accurately reflect the writer’s thought-process? Is there not an element of revision, polishing, and rhetoric in any essay? This doesn’t invalidate Knuth’s point, but thus far he does not seem to recognise the fictionality of the creative process. His WEB code is a story about how he wrote the program. What is the relationship between this story and the reality? Is there any reality that is not the story?

In the second case, his particular pattern of explanation didn’t work for everyone. In Knuth’s view, each part of the code should be preceded by the prose that ‘motivates’ the decision. Some in the group felt that it would be better to present the code, and follow it with a commentary, at least in some cases. But this would undermine the fiction that that code is emerging from a reasoning process that is reflected in the source.

Of course, we in the group bring our own assumptions and biases to the discussion. Knuth’s idea of the ‘essay’ may be perfectly valid, although it conflicts with ideas about literary composition that are popular in English departments. In particular, we dicussed the familiar nostrum of the ‘intentional fallcy’. Knuth makes little distinction between the programmer’s intention (or motivation) and the ‘meaning’ of the program. In Literature departments, we habitually distinguish the intention and the meaning: what the writer intended to say has really nothing to do with what they actually manage to say. As one member of the group observed, this notion of the ‘intentional fallacy’ reflects certain limitations in literary scholarship, especially the dominance of the nineteenth-century novel as a model for literature in general. Perhaps Knuth is right to tightly couple meaning and intention in the context of computer programming. The ‘author’ of a program is typically many people in conversation, unlike the distant ‘author’ of a triple-decker novel.

Against against intention: Amerikkkka, by Peli Grietzer.

An entire book written in WEB (or rather CWEB): MMIXware: A RISC Computer for the Third Millenium

The useless web?

We continue our reading of Literate Programming, by Donald Knuth.

We completed up to section 2 of Knuth’s web program to print the first n prime numbers. Having encountered the program definition, we have in some sense read the entire thing.

We did discuss whether modern code editors render Knuth’s entire notion of the ‘web of code’ otiose. We in particular considered EMACS, a code editor that was becoming popular at the time the paper was written.

EMACS stands for “editor macros,” and it basically allows a coder to write little programs that let them interact with their source code. The particular thing I was thinking of is the way you can use EMACS or similar programs to navigate your codebase. Say you come across a function called “check_if_prime” and you don’t know how it works. In EMACS you should be able to hit a keyboard shortcut, and be taken to the part of the source code where “check_if_prime” is defined, so you can see what it does. You should then be able to hit another keyboard shortcut to go back to where you were.

If you have a good code editor, is all the elaborate cross-referencing of a WEB program required?

The Quirk

We begin our reading of Literate Programming, by Donald Knuth.

For those who had to skip this meeting, we completed up to paragraph 2 on page 98. We will recommence in a fortnight at the line “Document formatting languages are newcomers to …”.

In answer to a query: Wikipedia informs me that LaTeX is a set of macros for the underlying TeX language. A macro is a procedure that modifies the text of a file. Thus the LaTeX program allows you to write directives into your document (e.g. \documentclass), which will then be translated by the LaTeX macros into the more basic TeX code. I was wrong to say that Knuth invented LaTeX – he invented TeX. LaTeX, with its increased functionality, was invented by Leslie Lamport. I can only assume that the “La” is for “Lamport”!

The ‘illiterate’ pascal files we saw at the start of the session can be seen here.