Add cellular-automata cave generator

Add a cellular-automata-based cave level generator, plus an
optparse-applicative-based CLI for invoking level generators in general.

src/Xanthous/Generators/Util.hs

@@ -0,0 +1,70 @@
+-- |
+
+module Xanthous.Generators.Util
+  ( Cells
+  , CellM
+  , randInitialize
+  , numAliveNeighborsM
+  , cloneMArray
+  ) where
+
+import Xanthous.Prelude
+import Data.Array.ST
+import Data.Array.Unboxed
+import Control.Monad.ST
+import Control.Monad.Random
+import Data.Monoid
+
+import Xanthous.Util (foldlMapM')
+import Xanthous.Data (Dimensions, width, height)
+
+type Cells s = STUArray s (Word, Word) Bool
+type CellM g s a = RandT g (ST s) a
+
+randInitialize :: RandomGen g => Dimensions -> Double -> CellM g s (Cells s)
+randInitialize dims aliveChance = do
+  res <- lift $ newArray ((0, 0), (dims ^. width, dims ^. height)) False
+  for_ [0..dims ^. width] $ \i ->
+    for_ [0..dims ^. height] $ \j -> do
+      val <- (>= aliveChance) <$> getRandomR (0, 1)
+      lift $ writeArray res (i, j) val
+  pure res
+
+numAliveNeighborsM
+  :: forall a i j m
+  . (MArray a Bool m, Ix (i, j), Integral i, Integral j)
+  => a (i, j) Bool
+  -> (i, j)
+  -> m Word
+numAliveNeighborsM cells (x, y) = do
+  cellBounds <- getBounds cells
+  getSum <$> foldlMapM'
+    (fmap (Sum . fromIntegral . fromEnum) . boundedGet cellBounds)
+    neighborPositions
+
+  where
+    boundedGet :: ((i, j), (i, j)) -> (Int, Int) -> m Bool
+    boundedGet ((minX, minY), (maxX, maxY)) (i, j)
+      | x <= minX
+        || y <= minY
+        || x >= maxX
+        || y >= maxY
+      = pure True
+      | otherwise =
+        let nx = fromIntegral $ fromIntegral x + i
+            ny = fromIntegral $ fromIntegral y + j
+        in readArray cells (nx, ny)
+
+    neighborPositions :: [(Int, Int)]
+    neighborPositions = [(i, j) | i <- [-1..1], j <- [-1..1], (i, j) /= (0, 0)]
+
+cloneMArray
+  :: forall a a' i e m.
+  ( Ix i
+  , MArray a e m
+  , MArray a' e m
+  , IArray UArray e
+  )
+  => a i e
+  -> m (a' i e)
+cloneMArray = thaw @_ @UArray <=< freeze