Fix X.emptysingletons

S.constant always evaluates its argument.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/Data/Array/Mixed/XArray.hs b/src/Data/Array/Mixed/XArray.hs
index 999ccc3..81b92c5 100644
--- a/src/Data/Array/Mixed/XArray.hs
+++ b/src/Data/Array/Mixed/XArray.hs
@@ -310,8 +310,10 @@ toList1 (XArray arr) = S.toList arr
 empty :: forall sh a. Storable a => IShX sh -> XArray sh a
 empty sh
   | Dict <- lemKnownNatRank sh
-  = XArray (S.constant (shxToList sh)
-                       (error $ "Data.Array.Mixed.empty: shape was not empty: " ++ show sh))
+  , shxSize sh == 0
+  = XArray (S.fromVector (shxToList sh) VS.empty)
+  | otherwise
+  = error $ "Data.Array.Mixed.empty: shape was not empty: " ++ show sh
 
 slice :: SNat i -> SNat n -> XArray (Just (i + n + k) : sh) a -> XArray (Just n : sh) a
 slice i n (XArray arr) = XArray (S.slice [(fromSNat' i, fromSNat' n)] arr)