Like chromatic, I have watched the recent irrational exuberance for domain-specific languages (DSLs) with bewilderment. In certain quarters of the programming universe, it seems that creating DSLs is nearly a rite of passage. The problem is, more and more of these DSLs appear to have been created mainly because, well, DSLs are cool these days, even if less “novel” solutions probably would have been more sensible.
Whereas chromatic unhesitatingly confronted the madness head-on, I have so far managed to avoid the fray. Sure, I’ve asked the occasional probing question of the DSL enthusiast, but mostly my reaction has been limited to standing back and staring in mute amazement at the runaway Domain-Specific Fun-Time Language Train, screaming down the tracks, destined for its inevitable high-speed derailment into what I can only expect will be a bridge abutment. But I’m starting to get the feeling that some of the train’s passengers are aboard because they think it’s the Right Thing To Do Train, so maybe it’s time to say something.
To set the record straight, I don’t have anything against DSLs, embedded or otherwise. (I have created my fair share, some of which are actually useful) No, my concern is limited strictly to the rise of the Gratuitous DSL. So let’s talk about it.
The reason – the right reason – for creating a DSL is because it ultimately lowers the cost of solving problems. If, then, you create a DSL and the cost of solving your problems does not go down, why did you create it? Think about it. Creating a DSL is an expensive proposition. Making people learn your DSL’s syntax, semantics, and underlying domain is a lot to ask – it’s costly. If you do ask, if you do make the imposition, you had better be sure your DSL pays its bills.
But what if your DSL turns out to be a deadbeat? What if using your DSL doesn’t lower the cost of solving problems? Well, guess what? You have created a Gratuitous Domain Specific Language.
Still unsure of whether you’re on the DSL Train for the wrong reason? No problem. Just take this simple, seven-step test:
Seven signs you may have created a Gratuitous Domain Specific Language (GDSL)
- You can’t actually explain what a DSL is.
- For your DSL, you can’t explain what the domain is.
- You have a hard time explaining the DSL’s syntax and semantics.
- You have a hard time explaining how the DSL interacts with the language it is embedded in. (For embedded DSLs only.)
- A vanilla library API would have captured the domain’s semantics without awkwardness.
- It’s easier to express complex domain concepts in general-purpose code than in your DSL.
- Your colleagues have a hard time writing things in your DSL.
Did more than a few of the statements ring true? If so, take a bow. You are the proud creator of a Gratuitous DSL!1
Even so, it’s not too late. You can always hop off the DSL Train at the next stop.
1. Rationale for the Seven Signs. Signs 1–4 suggest that your DSL may not even be a DSL. Signs 4–7 suggest that, though your DSL may be real, it may not be paying the bills.
Update: minor edit for clarity.
Update 2008-03-22: edits for clarity.