Hi, On Aug 5, 4:18 pm, michele <michelemen...@gmail.com> wrote: > ORIGINAL > > (defn update-positions [snake apple] > (dosync > (if (eats? @snake @apple) > (do (ref-set apple (create-apple)) > (alter snake move :grow)) > (alter snake move))) > nil) > > WITHOUT do > > (defn update-positions [snake apple] > (dosync > (if (eats? @snake @apple) > ((ref-set apple (create-apple)) <------ Removed "do" from > here > (alter snake move :grow)) > (alter snake move))) > nil) > > Both versions work, so why does the "do" on line 4 contribute?
It is an accident that the second version works. Probably create-apple returns a map. Replacing (create-apple) with - say - 5, should trigger an exception. The do is required, because you can have only one expression for the then-branch or the else-branch in an if. If you want to have several expressions in a branch you need a do, which executes each expression in a row and returns the value of the last one. So this is mostly useful for side effects. In the example the side effects are the calls to ref-set and alter. Hope this helps. Sincerely Meikel -- 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
