On 29 October 2014 11:01, Roelof Wobben <rwob...@hotmail.com> wrote: > > For a exercise I have to add something to the end of a existing map. > > So I thought this would work : > > (defn add-author [book new-author] > (assoc book (conj :authors new-author))) >
Take a look at that conj expression on its own: (conj :authors new-author) You're trying to conjoin "new-author" onto the keyword :authors, but keywords aren't collections. That's what the error means. It's saying that it expected a collection, but you've supplied a keyword instead. What you want is: (conj (get book :authors) new-author) Which can also be written: (conj (book :authors) new-author) (conj (:authors book) new-author) These two expressions are shortcuts for the above "get" function. They work because maps and keywords can act as functions. - James -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.