Fix space leak in System.Metric.Label.set

Author: arybczak

System/Metrics/Label.hs

@@ -12,7 +12,7 @@ module System.Metrics.Label
     , modify
     ) where
 
-import Data.IORef (IORef, atomicModifyIORef, newIORef, readIORef)
+import Data.IORef (IORef, atomicModifyIORef, atomicWriteIORef, newIORef, readIORef)
 import qualified Data.Text as T
 import Prelude hiding (read)
 
@@ -29,7 +29,7 @@ read = readIORef . unC
 
 -- | Set the label to the given value.
 set :: Label -> T.Text -> IO ()
-set (C ref) !i = atomicModifyIORef ref $ \ _ -> (i, ())
+set (C ref) !i = atomicWriteIORef ref i
 
 -- | Set the label to the result of applying the given function to the
 -- value.