This should be a function, not a macro. In fact it is just:
(defn multicmp [& xs] (first (remove zero? xs)))
But what you really wanted to begin with is a comparator function, so
more like:
(defn multicmp [& keys]
(fn [a b]
(or (first (remove zero? (map #(compare (% a) (% b))
keys)))
0)))
(sort-by (multicmp < =) coll)
On Dec 7, 5:51 pm, Andy Fingerhut <[email protected]> wrote:
> I've been going through the PLEAC web site, writing Clojure examples
> corresponding to the Perl code examples from the Perl Cookbook:
>
> http://pleac.sourceforge.net
>
> Michael Bacarella started a github repo to collect these together, and I'm
> helping flesh some of them out.
>
> https://github.com/mbacarella/pleac-clojure
>
> One thing that is very convenient in Perl is doing sorts on multiple
> comparison keys -- since 0 is treated as logically false in Perl, they can
> simply do what in Clojure would look like:
>
> (sort #(or (compare (key1 %1) (key2 %2))
> (compare (key2 %1) (key2 %2))
> ...)
> collection)
>
> This doesn't work in Clojure, because it only treats nil or false as
> logically false. It is easy to write a short-circuiting macro 'multicmp'
> that does the correct thing:
>
> (defmacro multicmp
> ([x] x)
> ([x & next]
> `(let [cmp# ~x]
> (if (not= cmp# 0)
> cmp#
> (multicmp ~@next)))))
>
> Then just replace 'or' in the first code snippet with 'multicmp'.
>
> Does something like this already exist in a library I'm unaware of? Would
> others find it useful to have around? And any suggestions on where it best
> belongs if so?
>
> Thanks,
> Andy
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