77 lines
3.1 KiB
Clojure
77 lines
3.1 KiB
Clojure
;; Functions to transform a world and run rules.
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(ns mw-engine.core
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(:require [mw-engine.world :as world]
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mw-engine.natural-rules
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mw-engine.utils))
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;; Every rule is a function of two arguments, a cell and a world. If the rule
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;; fires, it returns a new cell, which should have the same values for :x and
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;; :y as the old cell. Anything else can be modified.
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;;
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;; While any function of two arguments can be used as a rule, a special high
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;; level rule language is provided by the `mw-parser` package, which compiles
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;; rules expressed in a subset of English rules into suitable functions.
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;;
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;; A cell is a map containing at least values for the keys :x, :y, and :state;
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;; a transformation should not alter the values of :x or :y, and should not
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;; return a cell without a keyword as the value of :state. Anything else is
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;; legal.
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;;
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;; A world is a two dimensional matrix (sequence of sequences) of cells, such
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;; that every cell's :x and :y properties reflect its place in the matrix.
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;; See `world.clj`.
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;;
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;; Each time the world is transformed (see `transform-world`, for each cell,
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;; rules are applied in turn until one matches. Once one rule has matched no
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;; further rules can be applied.
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(defn- apply-rules
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"Derive a cell from this cell of this world by applying these rules."
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[cell world rules]
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(cond (empty? rules) cell
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true (let [result (apply (eval (first rules)) (list cell world))]
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(cond result result
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true (apply-rules cell world (rest rules))))))
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(defn- transform-cell
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"Derive a cell from this cell of this world by applying these rules. If an
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exception is thrown, cache its message on the cell and set state to error"
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[cell world rules]
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(try
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(apply-rules cell world rules)
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(catch Exception e (merge {:state :error :error (.getMessage e)} cell))))
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(defn- transform-world-row
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"Return a row derived from this row of this world by applying these rules to each cell."
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[row world rules]
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(map #(transform-cell % world rules) row))
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(defn transform-world
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"Return a world derived from this world by applying these rules to each cell."
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[world rules]
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(map
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#(transform-world-row % world rules)
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world))
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(defn- transform-world-state
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"Consider this single argument as a map of `:world` and `:rules`; apply the rules
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to transform the world, and return a map of the new, transformed `:world` and
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these `:rules`. As a side effect, print the world."
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[state]
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(let [world (transform-world (:world state) (:rules state))]
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(world/print-world world)
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{:world world :rules (:rules state)}))
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(defn run-world
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"Run this world with these rules for this number of generations.
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* `world` a world as discussed above;
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* `init-rules` a sequence of rules as defined above, to be run once to initialise the world;
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* `rules` a sequence of rules as definied above, to be run iteratively for each generation;
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* `generations` an (integer) number of generations."
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[world init-rules rules generations]
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(let [state {:world (transform-world world init-rules) :rules rules}]
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(take generations (iterate transform-world-state state))))
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