refactor(xan): Switch to V2 over tuples most places

These are generally rather nicer to work due to some typeclass instances,
and integrate better with other ecosystems for things like linear
algebra etc.

Change-Id: I546c8da7b17234648f3d612b28741c1fded25447
Reviewed-on: https://cl.tvl.fyi/c/depot/+/910
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/xanthous/src/Xanthous/Data.hs

@@ -28,6 +28,7 @@ module Xanthous.Data
   , loc
   , _Position
   , positionFromPair
+  , positionFromV2
   , addPositions
   , diffPositions
   , stepTowards
@@ -176,7 +177,7 @@ instance Num a => Group (Position' a) where
 -- | Positions convert to scalars by discarding their orientation and just
 -- measuring the length from the origin
 instance (Ord a, Num a, Scalar a) => Scalar (Position' a) where
-  scalar = fromIntegral . length . line (0, 0) . view _Position
+  scalar = fromIntegral . length . line 0 . view _Position
   fromScalar n = Position (fromScalar n) (fromScalar n)
 
 data Positioned a where
@@ -220,15 +221,18 @@ loc = iso hither yon
     hither (Position px py) = Location (px, py)
     yon (Location (lx, ly)) = Position lx ly
 
-_Position :: Iso' (Position' a) (a, a)
+_Position :: Iso' (Position' a) (V2 a)
 _Position = iso hither yon
   where
-    hither (Position px py) = (px, py)
-    yon (lx, ly) = Position lx ly
+    hither (Position px py) = (V2 px py)
+    yon (V2 lx ly) = Position lx ly
 
 positionFromPair :: (Num a, Integral i, Integral j) => (i, j) -> Position' a
 positionFromPair (i, j) = Position (fromIntegral i) (fromIntegral j)
 
+positionFromV2 :: (Num a, Integral i) => V2 i -> Position' a
+positionFromV2 (V2 xx yy) = Position (fromIntegral xx) (fromIntegral yy)
+
 -- | Add two positions
 --
 -- Operation for the additive group on positions
@@ -448,13 +452,13 @@ neighborDirections = Neighbors
 neighborPositions :: Num a => Position' a -> Neighbors (Position' a)
 neighborPositions pos = (`move` pos) <$> neighborDirections
 
-neighborCells :: Num a => (a, a) -> Neighbors (a, a)
+neighborCells :: Num a => V2 a -> Neighbors (V2 a)
 neighborCells = map (view _Position) . neighborPositions . review _Position
 
 arrayNeighbors
   :: (IArray a e, Ix i, Num i)
-  => a (i, i) e
-  -> (i, i)
+  => a (V2 i) e
+  -> V2 i
   -> Neighbors (Maybe e)
 arrayNeighbors arr center = arrLookup <$> neighborPositions (_Position # center)
   where