Working on getting drainage to actually work - which, inter alia, means

further work on efficiency.

src/mw_engine/core.clj

@@ -93,24 +93,6 @@
   * `generations` an (integer) number of generations.
 
   Return the final generation of the world."
-  [world init-rules rules generations]  
-  (let [state {:world (transform-world world init-rules) :rules rules}]
-    (:world 
-      (last 
-        (doall 
-          (take generations 
-                (iterate transform-world-state state)))))))
-
-(defn run-world2
-  "Doesn't work yet"
-  [world init-rules rules generations]
-  (with-local-vars [r (ref (transform-world world init-rules))]
-    (dotimes [g generations]
-      (dosync
-        (ref-set r (transform-world (deref r) rules))))
-    (deref r)))
-
-(defn run-world3
   [world init-rules rules generations]
   (reduce (fn [world _iteration]
             (transform-world world rules))

src/mw_engine/drainage.clj

@@ -2,9 +2,13 @@
 ;; assumed to have altitudes already set from a heighmap.
 
 (ns mw-engine.drainage
+  (:require
+    [clojure.core.reducers :as r])
   (:use mw-engine.utils
         mw-engine.world))
 
+(def ^:dynamic *sealevel* 10)
+
 (defn rain-world
   "Simulate rainfall on this `world`. TODO: Doesn't really work just now - should
    rain more on west-facing slopes, and less to the east of high ground"
@@ -16,12 +20,13 @@
   `cell` and for which this cell is the lowest neighbour"
   [world cell]
   (remove nil?
-          (map
+          (into []
+            (r/map
              (fn [n]
                (cond (= cell (get-least-cell (get-neighbours world n) :altitude)) n))
              (get-neighbours-with-property-value world (:x cell) (:y cell) 1
                                                                   :altitude
-                                                                  (or (:altitude cell) 0) >))))
+                                                                  (or (:altitude cell) 0) >)))))
 
 (defn flow
   "Compute the total flow upstream of this `cell` in this `world`, and return a cell identical
@@ -29,11 +34,14 @@
 
    Flow comes from a higher cell to a lower only if the lower is the lowest neighbour of the higher."
    [world cell]
+   (cond
+    (> (or (:altitude cell) 0) *sealevel*)
       (merge cell
            {:flow (+ (:rainfall cell)
                (apply +
                  (map (fn [neighbour] (:flow (flow world neighbour)))
-                      (flow-contributors world cell))))}))
+                      (flow-contributors world cell))))})
+    true cell))
 
 (defn flow-world
   "Return a world like this `world`, but with cells tagged with the amount of

src/mw_engine/utils.clj

@@ -36,7 +36,7 @@
   ([world function]
     (map-world world function nil))
   ([world function additional-args]
-    (into [] ;; vectors are more efficient for scanning, which we do a lot.
+    (into []
            (r/map (fn [row]
                     (into [] (r/map
                              #(apply function