Hello Will.
You can simplify it further:
1. Define a multimethod always dispatching by room id.
2. Create a :default implementation. It will be called for non-
fancy rooms.3. Create an implementation for :fancy-room. It will be
preferred over
:default for it.
If you ever have a group of rooms with a similar fancy description, use
a hierarchy
(derive :fancy-room1 :fancy-group)
(derive :fancy-room2 :fancy-group)
and create an implementation for :fancy-group.
Regards, Mikhail.
On Mon, 2 Apr 2018, at 19:39, Will Duquette wrote:
> 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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