Spent the weekend pondering all of this, and here's the way I think I want
to do it.
1. The world-state is stored in an atom, and updated much as Gary Johnson
suggests.
2. I define a multi-method, (describe-room [room world-state]), that is
responsible for computing the current description of the room: what it
looks like, what items are in it, whatever the player can currently see or
has just noticed.
3. The multi-method's dispatch function looks for the :description.
3a. If it's a string, the dispatch function returns nil; and I get the
default implementation: it describes the room in the simplest possible way.
3b. If the :description is undefined or nil, the dispatch function returns
the room's id, e.g., :fancy-room. The :fancy-room definition includes an
implementation of the multi-method that's specific to the :fancy-room. I
wouldn't expect to use this approach all that often, but it should be
flexible enough to do anything that comes up.
3c. If I find that I have a number of standard flavors for how to describe
a room, I can define the dispatch function accordingly and add additional
implementations.
There are other ways to skin this cat; but this one seems to give me
maximum simplicity for the normal case, maximum flexibility for special
cases, and it lets me keep all of the logic related to a single room in one
place in the code.
Comments?
On Thursday, March 29, 2018 at 3:45:02 PM UTC-7, Will Duquette 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?
>
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