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On DSLs and design patterns

Through an article on InfoQ I have come across a number of blog posts about DSLs (domain specific languages). It all starts with Joel (by now famous for his opinions on Ruby performance ;) ) who explains the rationale behind creating Wasabi, a DSL for his company's bug tracker. This software apparently has to run on VB and PHP.

InfoQ also refers to the blog "discipline and punish" (what a name) in which the author argues that DSLs are flawed due to their (or rather their creator's) inability to adapt to change - well, that's what I gather from it at least.

Personally, I am currently working for a company that has created its own DSL for describing user interfaces on mobile devices (we're not talking about simple XML, but rather a real language). These UIs need to run cross-platform (Symbian, MS Mobile, Java, etc) so the DSL really has to abstract the platform differences. So in essence, I really buy into Joel's argument that DSLs are about abstraction (I do NOT buy into his argument that Wasabi is a good idea for the reasons he describes or that creating a DSL would be not a lot of effort).

One thing that had not been covered on the DSL discussion as mentioned by InfoQ is the tools issue. If you create a DSL you either have to develop without tools (-> inefficient) or create your own tools (-> effort). For me, this is one of the reasons why I do think twice about creating a DSL and then think about it again.

And now to something completely different.

In this blog entry Mark Dominus argues that design patterns are a sign for a weakness in the language. Thought about it. Found it a brilliant observation. Agree. (and I'm sure Erich Gamma will not be happy ; )

Maybe there will always be design patterns because the mainstream general purpose languages changes so slowly (i.e. our change from one to the other). So we stick with them for a while (like a decade) until we learned enough to convert to a new general purpose language (think C, C++, Java).

Along these lines I remembered that the decorator pattern can be implemented really easily in Ruby. But still, it has to be implemented. So, maybe Ruby is not the great next thing after Java (it's just nice - which is good enough for me ;) ).

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