src/Grid.hs: define the Grid using "newtype" instead of "data".

diff --git a/src/Grid.hs b/src/Grid.hs
index f9a59729554a9f12d72d9e384f332e024e858bdc..761fdce1b8c924e472bf0d40ce9baa1439cb43bb 100644 (file)
--- a/src/Grid.hs
+++ b/src/Grid.hs
@@ -51,8 +51,8 @@ import Values ( Values3D, dims, empty3d, zoom_shape )
 --   values of the function at the grid points, which are distance h=1
 --   from one another in each direction (x,y,z).
 --
-data Grid = Grid { function_values :: Values3D }
-          deriving (Show)
+newtype Grid = Grid { function_values :: Values3D }
+                 deriving (Show)
 
 
 instance Arbitrary Grid where