Hi, Am 09.11.2009 um 20:08 schrieb Wilson MacGyver:
> (defn group [x] > (loop [newlist [] currlist x] > (if (not (empty? x)) > (recur (newlist (cons (first x) newlist)) > (currlist (drop-while #(= (first currlist) %) currlist)) > )))) > > > It seems logical to me, but when I tried it with > (group [1 1 2 2 3 3 ]) > > I get > CompilerException java.lang.IllegalArgumentException: Key must be > integer > > what am I missing? I think there is a misunderstanding how recur works. What you actually do, is to call newlist (a vector, acting as a function in this case). This is possible to retrieve the value at that index. ([1 2 3] 2) => 3. However you pass a Cons. Hence the exception. A non-lazy implementation with loop/recur is surprisingly ugly. You need two different loops: one to traverse the input list, one to count the number of occurrences of an item. Sincerely Meikel
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