Thanks James, But how do I use assoc with it
I tried this : (defn add-author [book new-author] (assoc book (conj (book :authors) new-author))) but then I see this message : ArityException Wrong number of args (2) passed to: core$assoc clojure.lang.AFn.throwArity (AFn.java:437) Roelof Op woensdag 29 oktober 2014 12:08:35 UTC+1 schreef James Reeves: > On 29 October 2014 11:01, Roelof Wobben <rwo...@hotmail.com <javascript:>> > 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.
