mustBeThawed :: String -> Worker -> IO ()
mustBeThawed m w = do t <- workerFrozen w
                      assert ("worker frozen unexpectedly: " ++ m) (not t) $ return ()
mustBeThawed :: String -> Worker -> IO ()
mustBeThawed m w = do t <- workerFrozen w
                      assert ("worker frozen unexpectedly: " ++ m) (not t) $ return ()
mustBeThawed m w = do t <- workerFrozen w
                      assert ("worker frozen unexpectedly: " ++ m) (not t) $ return ()