I’ve had to write a few domain-specific-languages in the past. As per Remy’s Law of Requirements Gathering, it’s been mostly because the users needed an Excel-like formula language. The danger of DSLs, of course, is that they’re often YAGNI in the extreme, or at least a sign that you don’t really understand your problem.

XML, coupled with schemas, is a tool for building data-focused DSLs. If you have some complex structure, you can convert each of its features into an XML attribute. For example, if you had a grammar that looked something like this:

Just last week, I was teaching a group of back-end developers how to use Angular to develop front ends. One question that came up, which did suprise me a bit, was how to deal with race conditions and concurrency in JavaScript.

I’m glad they asked, because it’s a good question that never occurred to me. The JavaScript runtime, of course, is single-threaded. You might use Web Workers to get multiple threads, but they use an Actor model, so there’s no shared state, and thus no need for any sort of locking.

Anonymous sends us this little blob of code, which is mildly embarassing on its own:

    static StringBuilder vsb = new StringBuilder();
    internal static string IsValidUrl(string value)
    {
        if (value == null)
        {
            return "\"\"";
        }

        vsb.Length= 0;
        vsb.Append("@\"");

        for (int i=0; i<value.Length; i++)
        {
            if (value[i] == '\"')
                vsb.Append("\"\"");
            else
                vsb.Append(value[i]);
        }

        vsb.Append("\"");
        return vsb.ToString();
    }

The progenitor of this story prefers to be called Mr. Syntax, perhaps because of the sins his boss committed in the name of attempting to program a spreadsheet-loader so generic that it could handle any potential spreadsheet with any data arranged in any conceivable format.

The boss had this idea that everything should be dynamic, even things that should be relatively straightforward to do, such as doing a web-originated bulk load of data from a spreadsheet into the database. Although only two such spreadsheet formats were in use, the boss wrote it to handle ANY spreadsheet. As you might imagine, this spawned mountains of uncommented and undocumented code to keep things generic. Sin was tasked with locating and fixing the cause of a NullPointerException that should simply never have occurred. There was no stack dump. There were no logs. It was up to Sin to seek out and destroy the problem.