Thank you all for your answers. The problem was caused by not starting the
REPL. I did not know that defmulti had defonce semantics.
On Sunday, February 22, 2015 at 7:04:58 PM UTC+1, Jeremy Heiler wrote:
>
> On 2/22/15 12:52 PM, Timur wrote:
> > Hi everyone,
> >
> > I have the following question regarding the defmultis of clojure:
> >
> > (defmulti create-fact
> > (fn [item-vector] (do
> > (print item-vector)
> > (first item-vector))))
> >
> > (defmethod create-fact [:a] [item-vector]
> > (str "a"))
> >
> > (defmethod create-fact [[:a "safs"]] [item-vector]
> > (str "safs"))
> >
> >
> > (mapv create-fact {:a "safs"})
> >
> >
> > Dispatch function is not called in this case and return is "safs" so the
> > matching key is [[:a "safs"]]. I except it to be :a, why is that [[:a
> > "safs"]]?
>
> First, observe:
>
> > (seq {:a 1 :b 2})
> ([:a 1] [:b 2])
>
> A map is converted into a sequence with each element being a key/value
> pair. The mapv function does this under the hood so that it can operate
> on the map as a sequence.
>
> Now, when I run your code, I get an IllegalArgumentException stating
> that :a is not a dispatch value. This is correct, because the two
> dispatch values defined are [:a] and [[:a "safs"]]. If you change the
> [:a] method to be :a, then the return value will be "a". The dispatch
> values in each defmethod must be literal, and not wrapped in a vector
> like when defining the arguments to a fn.
>
> Does that clear things up?
>
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