> 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?
The do is there because if takes the form (if pred then else), and in this case the "then" is supposed to be two statements executed for side-effects. Removing the do form would actually result in something different than above; what you've done is replaced a (do form1 form2) with a ((form1) form2). In other words, you're calling (ref-set apple (create-apple)), and then *calling the return value of that* with the parameter (alter snake move :grow). Why this seems to work I don't know without looking at the snake example, but presumably (create-apple) creates an apple, and presumably an "apple" is something which is callable (probably a map, so that when called with the return-value of (alter snake move) it simply returns nil or some value associated with that key). -- / Peter Schuller -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to [email protected] Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/clojure?hl=en
