A set might be better to hold the player-refs, then you can just call (disj player-refs player-ref) without doing any extra checking.
Also you can access ref values without needing to be in a dosync. Things being immutable, the value you get from, say, @team-ref won't change once you have it. On Jul 5, 5:12 pm, Mark Volkmann <r.mark.volkm...@gmail.com> wrote: > I wrote some fairly simple code to demonstrate use of StructMaps and > Refs. It's 80 lines including comments. I'd appreciate it if someone > could look it over and let me know if I've done anything that isn't > very idiomatic. > > The program models sports teams and players. The main functionality is > the ability to trade sets of players between teams. Both teams and > players are held by Refs. Players have a reference to their team. > Teams have references to their players. > > The output from the code follows: > > Before trade: > Oilers roster: > Wayne Gretzky > Mike Krushelnyski > Marty McSorley > Kings roster: > Jimmy Carson > Martin Gelinas > > After trade: > Oilers roster: > Martin Gelinas > Jimmy Carson > Kings roster: > Wayne Gretzky > Mike Krushelnyski > Marty McSorley > > Here's the code: > > ; A player knows his team, if any. > (defstruct player-struct :name :team-ref) > > ; A team knows its players. > (defstruct team-struct :name :player-refs) > > ; Makes a new Ref to a player-struct that isn't on any team. > (defn make-player [name] > (ref (struct player-struct name))) > > ; Makes a new Ref to a team-struct that contains no players. > (defn make-team [name] > (ref (struct team-struct name []))) > > (defn assign-player-to-team [player-ref new-team-ref] > (dosync > ; If the player has a former team, remove them from it. > (if-let [old-team-ref (@player-ref :team-ref)] > (let [old-player-refs (@old-team-ref :player-refs) > new-player-refs (remove #(= % player-ref) old-player-refs)] > (alter old-team-ref assoc :player-refs new-player-refs))) > > ; Add the player to their new team. > (let [old-player-refs (@new-team-ref :player-refs) > new-player-refs (conj old-player-refs player-ref)] > (alter player-ref assoc :team-ref new-team-ref) > (alter new-team-ref assoc :player-refs new-player-refs)))) > > ; Returns a string describing a given player. > (defn player-to-string [player-ref] > (dosync > (str (@player-ref :name) " plays for " > (if-let [team-ref (@player-ref :team-ref)] > (str "the " (@team-ref :name)) > "nobody") > "."))) > > ; Returns a string describing a given team. > (defn team-to-string [team-ref] > (dosync > (apply str > (@team-ref :name) " roster:" > (map > (fn [player-ref] (str "\n " (@player-ref :name))) > (@team-ref :player-refs))))) > > ; players1 and players2 are collections of Refs to player StructMaps. > ; Neither can be empty. > ; All players in a collection must be on the same team. > (defn trade [players1 players2] > (dosync > (let [team1 ((first players1) :team-ref) > team2 ((first players2) :team-ref)] > (doseq [p players1] > (assign-player-to-team p team2)) > (doseq [p players2] > (assign-player-to-team p team1))))) > > (let [oilers (make-team "Oilers") > kings (make-team "Kings") > p1 (make-player "Wayne Gretzky") > p2 (make-player "Mike Krushelnyski") > p3 (make-player "Marty McSorley") > p4 (make-player "Jimmy Carson") > p5 (make-player "Martin Gelinas")] > > (doseq [p [p1 p2 p3]] > (assign-player-to-team p oilers)) > (doseq [p [p4 p5]] > (assign-player-to-team p kings)) > > (println "Before trade:") > (println (team-to-string oilers)) > (println (team-to-string kings)) > > (trade [p1 p2 p3] [p4 p5]) > > (println "\nAfter trade:") > (println (team-to-string oilers)) > (println (team-to-string kings))) > > -- > R. Mark Volkmann > Object Computing, Inc. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
