121 lines
4.5 KiB
Clojure
121 lines
4.5 KiB
Clojure
;; Functions to transform a world and run rules.
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(ns mw-engine.core
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(:use mw-engine.utils)
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(:require [clojure.core.reducers :as r]
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[mw-engine.world :as world])
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(:gen-class))
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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-rule
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"Apply a single `rule` to a `cell`. What this is about is that I want to be able,
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for debugging purposes, to tag a cell with the rule text of the rule which
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fired (and especially so when an exception is thrown. So a rule may be either
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an ifn, or a list (ifn source-text). This function deals with despatching
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on those two possibilities. `world` is also passed in in order to be able
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to access neighbours."
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([world cell rule]
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(cond
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(ifn? rule) (apply-rule cell world rule nil)
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(seq? rule) (let [[afn src] rule] (apply-rule cell world afn src))))
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([cell world rule source]
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(let [result (apply rule (list cell world))]
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(cond
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(and result source) (merge result {:rule source})
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true result))))
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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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[world cell rules]
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(cond (empty? rules) cell
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true (let [result (apply-rule world cell (first rules))]
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(cond result result
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true (apply-rules world cell (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 it's state to error"
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[world cell rules]
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(try
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(merge
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(apply-rules world cell rules)
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{:generation (+ (or (:generation cell) 0) 1)})
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(catch Exception e
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(merge cell {:error
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(format "%s at generation %d when in state %s"
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(.getMessage e)
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(:generation cell)
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(:state cell))
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:state :error}))))
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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-world world transform-cell (list rules)))
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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 defined above, to be run iteratively for each generation;
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* `generations` an (integer) number of generations.
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Return the final generation of the world."
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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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(:world
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(last
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(doall
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(take generations
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(iterate transform-world-state state)))))))
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(defn run-world2
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"Doesn't work yet"
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[world init-rules rules generations]
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(with-local-vars [r (ref (transform-world world init-rules))]
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(dotimes [g generations]
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(dosync
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(ref-set r (transform-world (deref r) rules))))
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(deref r)))
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(defn run-world3
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[world init-rules rules generations]
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(reduce (fn [world _iteration]
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(transform-world world rules))
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(transform-world world init-rules)
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(range generations)))
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