44 lines
1.4 KiB
Plaintext
44 lines
1.4 KiB
Plaintext
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(ns jeremy-website.l-system)
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;; TODO support context-sensitive grammers? This is where a production
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;; rule can apply only if the symbol in question occurs between
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;; specific other symbols
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(defn rules-for-symbol
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[symbol rules]
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(filter #(= (:predecessor %) symbol) rules))
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(defn choose-rule [random-fn rules]
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(let [random (random-fn)
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iter-fn (fn [[rule & rules] current-prob]
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(cond
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(nil? rule) nil
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(< random (+ current-prob
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(:probability rule))) rule
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:else (recur rules (+ current-prob
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(:probability rule)))))
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selected (iter-fn rules 0)]
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(or selected (first rules))))
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(defn apply-rules
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[rules random-fn symbol]
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(let [rules-for-symbol (rules-for-symbol symbol rules)
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selected-rule (choose-rule random-fn rules-for-symbol)]
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(if selected-rule
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(:successor selected-rule)
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[symbol])))
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(defn step
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"Applies the l-system rules once"
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[{:keys [rules state random-fn] :as l-system}]
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(let [new-state (mapcat (partial apply-rules rules random-fn) state)]
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(assoc l-system :state (vec new-state))))
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(defn instantiate
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"Instantiates a new L-system"
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[{:keys [rules axiom random-fn] :or {random-fn rand}}]
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{:rules rules
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:axiom (vec axiom)
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:state (vec axiom)
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:random-fn random-fn})
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