Showing posts with label dsl. Show all posts
Showing posts with label dsl. Show all posts
Friday, June 5, 2009
Sunday, May 17, 2009
The Need for More Lack of Understanding
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A recent post by Gilad Bracha echoed with my experience designing two small internal DSL in Clojure (Moustache and Enlive's selectors).
It's not the same kind of non-understanding which I have in mind. I'm talking about a macro/DSL being able to not understand what is passed to it.
I think it's an important feature for the user to be able to get out of your DSL and back in regular Clojure.
In both Moustache and Enlive, I avoid to give a special meaning to lists (in Clojure you also have vectors, maps and sets), hence lists always denote user-code and are embedded as-is in the macro expansion. (If I really had to use lists for a DSL, I would check a list doesn't start with a special value (eg do or unquote (~) — thanks to MB's comment) before processing it).
That's why in Enlive you can easily add your own selectors step [:p (my-selector-step arg1 arg2)] as long as (my-selector-step arg1 arg2) evaluates to a correct value (here a state machine).
That's also how Moustache supports wrapping another Ring handler or custom route validation.
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