There's no way to make that work currently. Whether it should work requires
some discussion but at the moment I'm inclined to say no.
On Wednesday, November 14, 2012, David Jagoe wrote:
> Hi all,
>
> I have a core.match pattern that looks something like this:
>
> (def !nil? (complement nil?))
>
> (match [*a* *b*]
> [(a :guard !nil?) nil] (dosomething a)
> [nil (b :guard !nil?)] (dosomething b)
> [(a :guard !nil?) (b :guard !nil?)] (dosomething a b)
> :else (throw (Exception. "Not allowed"))
>
> The point is that in every case I guard the variable using !nil?
>
> I would like to shorten my code:
>
> (match [*a* *b*]
> [(!nil a) nil] (dosomething a)
> [nil (!nil b)] (dosomething b)
> [(!nil a) (!nil b) (dosomething a b)
> :else (throw (Exception. "Not allowed"))
>
> But I can't figure out how to write the !nil macro.
>
> I've tried:
>
> (defmacro notnil [sym]
> `(~sym :guard (complement nil?)))
>
> Which looks right in expansion:
>
> (macroexpand-1 '(!nil foo))
> -> (foo :guard (clojure.core/complement clojure.core/nil?))
>
> But I cannot use this in a match:
>
> (let [foo nil bar 2]
> (match [foo bar]
> [(!nil foo) 2] foo
> :else :notfound))
> CompilerException java.lang.AssertionError: Invalid list syntax foo in
> (!nil foo)
>
> Why!!?!??!
>
> I guess its got something to do with the fact that match itself is a macro?
>
> Is there some other way that I could extend match to only match when the
> variable is not nil?
>
> Thanks,
> David
>
>
>
> --
> David Jagoe
>
> davidja...@gmail.com <javascript:_e({}, 'cvml', 'davidja...@gmail.com');>
> +18053284389
>
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