You want to think more abstractly. What are the common elements in your
code?
For instance, a naive first pass:
(defn move [subject delta]
(update-in subject [:position] v+ delta))
(defn key-held [key]
(@*keys-held* :left))
(defmacro on [subject event action]
`(if ~event (-> ~subject ~action))
Then you could write:
(-> g
(on (key-held :left) (move [-10 0]))
(on (key-held :right) (move [10 0]))
(on (key-held :up) (move [0 -10]))
(on (key-held :down) (move [0 10]))
But if you're designing a game, you usually want to separate the event loop
from the event handling. That's a big topic though, and I can't really go
into much detail in a single post.
- James
On 11 February 2013 20:10, JvJ <[email protected]> wrote:
> I'm writing a simple game engine in Clojure, and each game object supplies
> its own unique update function, which takes the original object (a map of
> properties) and returns an updated version. However, writing the updates
> is somewhat cumbersome because each line of code has to return either the
> original or updated object. I'd like to see if I can clean up this code,
> possibly by using monads (which I don't understand very well). Does anyone
> have any advice? Thanks (Code examples below)
>
> The pseudocode for what i want to do looks something like this:
>
> if left key is held
> g.position += [-10 0]
> if right key is held
> g.position += [10 0]
> if up key is held
> g.position += [0 -10]
> if down key is held
> g.position += [0 10]
> if q is pressed
> fire event {:type :dialogue, :text "Hello"}
> if space is pressed
> g.switchstate(:s2)
>
>
> But the code I ended up writing is this mess:
>
>
> (fn [g]
> (-> g
> (#(if (@*keys-held* :left)
> (update-in % [:position] v+ [-10 0])
> %))
> (#(if (@*keys-held* :right)
> (update-in % [:position] v+ [10 0]) %))
> (#(if (@*keys-held* :up)
> (update-in % [:position] v+ [0 -10]) %))
> (#(if (@*keys-held* :down)
> (update-in % [:position] v+ [0 10]) %))
> (#(if (@*keys-pressed* \q)
> (do (fire-event {:type :dialogue
> :text "Hello!"})
> %)
> %))
> (#(if (@*keys-pressed* :space)
> (do (comment (println "spaced!"))
> (switch-state % :s2)) %))))
>
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