# Talk:GHC/Type families

### From HaskellWiki

I believe the instance declaration:

instance GMapKey Int where

data GMap Int v = GMapInt (Data.Map.Map Int v) empty = GMapInt Data.Map.empty lookup k (GMapInt m) = Data.Map.lookup k m insert k v (GMapInt m) = GMapInt (Data.Map.insert k v m)

should be:

instance GMapKey Int where

data GMap Int v = GMap Int (Data.Map.Map Int v) empty = GMap Int Data.Map.empty lookup k (GMapInt m) = Data.Map.lookup k m insert k v (GMapInt m) = GMap Int (Data.Map.insert k v m)