Commit before trying IntMap instead of vector for incidence graph

src/Loop.hs

@@ -76,7 +76,8 @@ doLoop spf window worldSideEffects eventFn startWorld = do
     maybeUpdatedWorld <- pollEvents >>= foldM (applyEventIO eventFn) (Just worldAfterSimStep)
     case maybeUpdatedWorld of
         Just updatedWorld -> do
-            performGC
+            performGC -- potentially use performMinorGC
+--  https://stackoverflow.com/questions/30244139/how-to-keep-very-big-elements-on-memory-without-exhausting-the-garbage-collector
             endTicks <- ticks -- it might be better to use System.Clock (monotonic)
             let theDelay = max 0 (spf + fromIntegral startTicks - fromIntegral endTicks)
             threadDelay (theDelay * 1000)