Add a cube_at function to Grid.

diff --git a/src/Grid.hs b/src/Grid.hs
index 6d360e2c103d61cc6b41a9cc3873f52db756e169..3ca66ca7ddbde546bec6080b55637306b5232e8f 100644 (file)
--- a/src/Grid.hs
+++ b/src/Grid.hs
@@ -45,3 +45,17 @@ cubes g
       zsize = (length fvs) - 1
       ysize = (length $ head fvs) - 1
       xsize = (length $ head $ head fvs) - 1
+
+
+-- | Takes a grid and a position as an argument and returns the cube
+--   centered on that position. If there is no cube there (i.e. the
+--   position is outside of the grid), it will return Nothing.
+cube_at :: Grid -> Int -> Int -> Int -> Maybe Cube
+cube_at g i j k
+    | i < 0 = Nothing
+    | j < 0 = Nothing
+    | k < 0 = Nothing
+    | i >= length (cubes g) = Nothing
+    | j >= length ((cubes g) !! i) = Nothing
+    | k >= length (((cubes g) !! i) !! j) = Nothing
+    | otherwise = Just $ (((cubes g) !! i) !! j) !! k