Only allow adjacent gormlaks to attack

Previously the isUnit function was falsely returning `True` for
positions that were one tile off in *either* direction from the
character, when it should've been *both*. Oops.

2 files changed, 10 insertions, 2 deletions

diff --git a/src/Xanthous/Data.hs b/src/Xanthous/Data.hs
index ff11a8da7f80..b7df191e58a8 100644
--- a/src/Xanthous/Data.hs
+++ b/src/Xanthous/Data.hs
@@ -136,7 +136,8 @@ diffPositions (Position x₁ y₁) (Position x₂ y₂) = Position (x₁ - x₂)
 --
 -- ∀ dir :: Direction. isUnit ('asPosition' dir)
 isUnit :: Position -> Bool
-isUnit (Position px py) = abs px == 1 || abs py == 1
+isUnit (Position px py) =
+  abs px `elem` [0,1] && abs py `elem` [0, 1] && (px, py) /= (0, 0)
 
 --------------------------------------------------------------------------------
 
diff --git a/test/Xanthous/DataSpec.hs b/test/Xanthous/DataSpec.hs
index 6b94e6a0582a..26a862baa6a6 100644
--- a/test/Xanthous/DataSpec.hs
+++ b/test/Xanthous/DataSpec.hs
@@ -26,7 +26,14 @@ test = testGroup "Xanthous.Data"
         directionOf pos (move dir pos) == dir
     , testProperty "diffPositions is add inverse" $ \pos₁ pos₂ ->
         diffPositions pos₁ pos₂ == addPositions pos₁ (invert pos₂)
-
+    , testGroup "isUnit"
+      [ testProperty "double direction is never unit" $ \dir ->
+          not . isUnit $ move dir (asPosition dir)
+      , testCase "examples" $ do
+          isUnit (Position 1 1) @? "not . isUnit $ Position 1 1"
+          isUnit (Position 0 (-1)) @? "not . isUnit $ Position 0 (-1)"
+          (not . isUnit) (Position 1 13) @? "isUnit $ Position 1 13"
+      ]
     ]
   , testGroup "Direction"
     [ testProperty "opposite is involutive" $ \(dir :: Direction) ->