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| -rw-r--r-- | Utility/Monad.hs | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Utility/Monad.hs b/Utility/Monad.hs index 0d1675fa4..9e2a16e8c 100644 --- a/Utility/Monad.hs +++ b/Utility/Monad.hs @@ -28,3 +28,11 @@ anyM p = liftM isJust . firstM p {- Runs an action on values from a list until it succeeds. -} untilTrue :: (Monad m) => [a] -> (a -> m Bool) -> m Bool untilTrue = flip anyM + +{- Runs a monadic action, passing its value to an observer + - before returning it. -} +observe :: (Monad m) => (a -> m b) -> m a -> m a +observe observer a = do + r <- a + _ <- observer r + return r |