Exploration Through Example

Example-driven development, Agile testing, context-driven testing, Agile programming, Ruby, and other things of interest to Brian Marick
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Sun, 25 Jan 2004

Code-reading practices

My first event in the Master of Fine Arts in Software trial run was a lecture on code-reading in the style of the literary critic Stanley Fish. His "affective stylistics" has one read a poem (say) word-by-word, asking what each word does for the reader. What expectations does it set up? or overturn? What if that word were omitted or moved elsewhere? (I've written on a similar topic earlier, and I drew my examples from that entry.)

I compared idiomatic Lisp code, "C-like" Lisp code, idiomatic C code, and Lisp-like C code to show how expectations and membership in "interpretive communities" influence readability. In the process, I learned something unexpected.

I presented code like this to Dick Gabriel, expecting he would think it an idiomatic recursive implementation of factorial.

(defun fact(n &optional (so-far 1))
   (if (<= n 1)
      (fact (- n 1) (* n so-far)))

Note: because of my presentation's structure, I originally named the function f so as not to give away immediately that it was factorial. I don't think that's germane to this note, so I'm giving it the clearer name here.

He didn't think it was idiomatic, not really. He found it somewhat old-fashioned, preferring an implementation that replaces the optional argument with an internal helper function (introduced by the labels form).

      (defun fact (n)
        (labels ((f (n acc)
                   (if (<= n 1) acc (f (- n 1) (* n acc)))))
            (f n 1)))

Now, I always hated labels. What's the difference between Dick and me? It appears to be reading style. As I understand it from him, truly idiomatic Lisp reading style goes like this:

  1. Look for a key name (fact(n)).

  2. Quickly skip down to the code of maximum density.

               (if (<= n 1) acc (f (- n 1) (* n acc)))))
    That's the important code. If that's not clear, find the declarations that clarify it by scanning upward. The most important ones will be nearby.

The labels version of the code fits that. The reading style and writing style are "tuned" to each other. It does not fit my reading style, which is to read linearly through functions (though I do bounce around among functions). So the labels verbiage at the front slows me down. I expect the interior names to be more intention-revealing than they need to be when they're just placeholders to make interesting ideas invokable. Because I don't know the visual cues that say "Pay attention here!", I may do more memorization of facts that turn out to be unimportant.

It's arguable that my reading style is just flat-out worse, but I do think that tuning reading to writing is a more useful way to think about it.

All this may seem small, but it reinforces my idea that attending closely to the act of reading will yield some Aha! moments to improve our practice.

## Posted at 10:41 in category /mfa [permalink] [top]

About Brian Marick
I consult mainly on Agile software development, with a special focus on how testing fits in.

Contact me here: marick@exampler.com.




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