Often it's better to store the entire game state as one large, immutable data structure.
Atoms are usually preferred over refs in most cases. When you want polymorphism over a map, the most common solution is to use protocols and records. On 29 March 2018 at 23:45, Will Duquette <w...@wjduquette.com> wrote: > I'm an experienced programmer, but a Clojure newbie; as a beginner > project, I'm looking into how one would idiomatically write a text > adventure of sorts in Clojure. I'm less interested in producing a playable > game than I am in learning how to do such a thing in a proper functional > style. > > Suppose in this game I have a room whose description changes based on a > global flag. For example, there's something in the Fancy Room that you > won't notice until you've reached the major plot point. > > The world map is (for the sake of argument) a hash-map whose keys are the > room IDs and whose values are room records, where each record is a hash-map. > > (def world {:fancy-room {:name "Fancy Room" :description "This is a fancy > room." ...}}) > > I'm aware that I could use a (defstruct) or (defrecord); I'm keeping it > simple for now. Then, the flags are saved in a ref; the intent is that > mutable set is segregated, so that it can more easily be written to a save > file. > > ;; Global set of flags > (def flags (ref #{}) > > (defn flag-set [flag] > (dosync (alter flags conj flag)) > > ;; When the major plot point is reached > (flag-set :major-plot-point-reached) > > Normally, to describe a room you just return its :description. > > (defn describe [room] (:description (world get room))) > > But for the :fancy-room, the returned description depends on the global > flag, and it will be specific to :fancy-room. I could add this logic > directly to the (describe) function's body, but that would be ugly. What > I'd like to do is attach a lambda to the :fancy-room in some way. The > (describe) function looks for a :describer, and if it's there it calls it; > and if not it just returns the :description: > > (defn describe [entity] > (if (:describer entity) > ((:describer entity) entity) > (:description entity))) > > *Question 1*: this works, but it looks ugly to me; I figure there's a > better, more idiomatic way to do this kind of thing that's probably obvious > to anyone with any real experience. Multimethods, maybe? Define a Room > protocol, then let most rooms be NormalRoom records, but let :fancy-room be > a FancyRoom record? > > *Question 2*: Whatever code actually computes the description, it will > need access to the :major-plot-point-reached flag. What's the cleanest way > to give the description code access to the flags ref? It could simply > access "@flags" directly: > > (if (:major-plot-point-reached @flags) > "This is a fancy room. Hey, that light sconce looks movable!" > "This is a fancy room.") > > But that doesn't seem properly functional. Would it be better to pass the > game state into each method? > > (defn describe [entity state] > (if (:describer entity) > ((:describer entity) entity state) > (:description entity))) > > Any ideas? > > -- > 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. > -- James Reeves booleanknot.com -- 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.