num for entropy

1 files changed, 1 insertions, 0 deletions

diff --git a/Cost.hs b/Cost.hs
index 5fd003f..99baa33 100644
--- a/Cost.hs
+++ b/Cost.hs
@@ -58,6 +58,7 @@ type CostCalc op t = Entropy t -> Cost op
 
 -- | Number of bits of entropy
 newtype Entropy t = Entropy Int
+	deriving (Num)
 
 -- | Entropy can never go negative when subtracting bits from it.
 reduceEntropy :: Entropy t -> Int -> Entropy t