The Allure of the Asymmetrical

Though I’ve lived in Charlottesville for two years, I haven’t taken enough advantage of the local farms. I obsess over health, and grass-fed animal products abound in the area. But when I finally patronized a farm last week, I noticed something obvious¹. Local eggs look nicer than their industrial-farm begotten counterparts.

The local eggs appeal to my eye not due to differences in color or lighting, but through asymmetry. If you look at them closely, you see a deviation in size across the carton, a variance in color, and a sprinkling of freckles across shell exteriors. They are skewed, chaotic. In contrast, it looks like someone bleached the industrial eggs, which vary little in size across the carton.

A slight asymmetry plays nice with human perception. It draws our eyes to important details, yet makes it easier for us to perceive the whole. Asymmetrical perception may have implications for how we write code².

Consider this comparison of a C function (taken sort-of randomly from Git) and a Clojure function (taken from Gajure). First let’s look at add_files_to_cache:

int add_files_to_cache(const char **prefix, const char **pathspec, int flags)  
{  
    struct update_callback_data data;  
    struct rev_info rev;  
    init_revisions(&rev, prefix);  
    setup_revisions(0, NULL, &rev, NULL);  
    rev.prune_data = pathspec;  
    rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;  
    rev.diffopt.format_callback = update_callback;  
    data.flags = flags;  
    data.add_errors = 0;  
    rev.diffopt.format_callback_data = &data;  
    run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);  
    return !!data.add_errors;  
}

Reading from the left, this function is symmetrical. It doesn’t draw the eye to any particular bit of code within the curly braces, and it doesn’t convey anything through it’s structure. Much of this has to do with the imperative nature of C and add_files_to cache. Now consider a second function, list-crossover:

(defn list-crossover  
    “A generic crossover function for simple lists. 
    You may need to write your own.”  
    [[s1 s2]]  
        (let [point (rand-int  
                        (min (count s1)  
                        (count s2)))]  
            (concat 
                (take point s1)  
                (drop point s2))))

Here you see a nesting of sorts, as indentation conveys properties in the code (e.g. that take and drop are arguments to concat). The functional nature of Clojure lends itself well to this kind of visual deconstruction, and list-crossover imparts semantic meaning through asymmetrical structure.

I don’t suggest that one language is better than another at conveying meaning through syntax and symmetry, but rather that the way you write code has implications upon how easily it’s understood. Symmetry, or a lack thereof, plays an important role.