io-sim: inline on in Eq instance of TVar

Author: coot

io-sim/src/Control/Monad/IOSim/CommonTypes.hs

@@ -10,7 +10,6 @@ module Control.Monad.IOSim.CommonTypes where
 import           Control.Monad.Class.MonadSTM (TraceValue)
 import           Control.Monad.ST.Lazy
 
-import           Data.Function (on)
 import           Data.Map (Map)
 import           Data.Set (Set)
 import           Data.STRef.Lazy
@@ -76,7 +75,7 @@ data TVar s a = TVar {
      }
 
 instance Eq (TVar s a) where
-    (==) = on (==) tvarId
+    TVar {tvarId = a} == TVar {tvarId = b} = a == b
 
 data SomeTVar s where
   SomeTVar :: !(TVar s a) -> SomeTVar s