Day 21, with major part a cleanups and improved comments.

src/AOC-21b.hs

@@ -20,13 +20,14 @@ splits = M.assocs $ roll 3 (M.singleton 0 1) where
 universes :: Array (Int,Int,Int,Int) (Integer,Integer)
 universes = array bds [(p, score p) | p <- range bds] where
   bds = ((0,1,0,1),(20,10,20,10))
-  score (xScore,xPos,yScore,yPos) = sumPairs
-                    [ (c * losers, c * winners)
-                    | (r,c) <- splits
-                    , let nPos = ((xPos + r - 1) `mod` 10) + 1
-                          nScore = xScore + nPos
-                          (winners,losers) = univ yScore yPos nScore nPos
-                    ]
+  score (xScore,xPos,yScore,yPos) = 
+    sumPairs
+      [ (c * losers, c * winners)
+      | (r,c) <- splits
+      , let nPos = ((xPos + r - 1) `mod` 10) + 1
+            nScore = xScore + nPos
+            (winners,losers) = univ yScore yPos nScore nPos
+      ]
   sumPairs = foldr1 (\(a,b) (c,d) -> (a+c,b+d))
   univ xScore xPos yScore yPos
     | yScore >= 21 = (1,0)