I've got a single moving square and a small pile of Clojure written so far, but now what I want to do is have a collection of moving squares because no game of Space Invaders is complete without aliens, and last I checked there was more than one of them.
Well, if I want lots of squares I'm going to have to look at some means of representing collections in Clojure and my searches take me to Sequences
To create a sequence, I can do something like this
(defn createSeq  (for [x [0 1 2 3]] x ) )
Which returns me a sequence containing 0 1 2 3, an important point here is (at least I think), is that this sequence is lazy, it has not been executed yet.
Now, my collection of invaders will actually be 2D, so what I can actually do is
(defn createSeq  (for [x [0 1 2 3] y [0 1 2 3]] [x y] ) )
Which returns me a sequence containing lots of [x y] pairs, so [0 0] [0 1] [0 2] etc.
Of course, there are functions for me here, so I can make a range
(defn createSeq  (for [x (range 0 100 10) y (range 0 100 10)] [x y] ) )
Pretty nifty if I do say so myself, so what I can start with if I want to draw a grid of yellow squares is something like
(defn initState  (for [x (range 0 100 10) y (range 0 100 10)] [x y] ) )
And I can call my initial tick method, passing in this state
(defn ^:export init  (tick (initState)) )
And then loop through this
(defn tick [enemies] (let [ctx (context)] (clearScreen ctx) (doseq [[x y] enemies] (drawSquare ctx x y 5 5)) (js/setTimeout (fn  (tick enemies) ) 33 ) ) )
Note that I'm able to expand the content of this sequence as part of the doseq call
(doseq [[x y] enemies] (drawSquare ctx x y 5 5))
Gotta like that at least a little bit!
About this doseq, this doseq is explicitly created to allow for side effects, I could have done
(for [[x y] enemies] (drawSquare ctx x y 5 5))
But nothing would happen because this is lazy too - had my head scratching for a while on that one...
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