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1. adjustWithKey :: IsMap map => (ContainerKey map -> MapValue map -> MapValue map) -> ContainerKey map -> map -> map

   mono-traversable	Data.Containers

   Equivalent to adjustMap, but the function accepts the key, as well as the previous value.

2. fromJust :: Maybe a -> a

   strict	Data.Strict.Maybe

   Extracts the element out of a Just and throws an error if the argument is Nothing.

3. isJust :: Maybe a -> Bool

   strict	Data.Strict.Maybe

   Yields True iff the argument is of the form Just _.

4. untilJust :: Monad m => m (Maybe a) -> m a

   monad-loops	Control.Monad.Loops

   Run the supplied Maybe computation repeatedly until it returns a value. Returns that value.

5. whileJust :: Monad m => m (Maybe a) -> (a -> m b) -> m [b]

   monad-loops	Control.Monad.Loops

   As long as the supplied Maybe expression returns "Just _", the loop body will be called and passed the value contained in the Just. Results are collected into a list.

6. whileJust' :: (Monad m, MonadPlus f) => m (Maybe a) -> (a -> m b) -> m (f b)

   monad-loops	Control.Monad.Loops

   As long as the supplied Maybe expression returns "Just _", the loop body will be called and passed the value contained in the Just. Results are collected into an arbitrary MonadPlus container.

7. whileJust_ :: Monad m => m (Maybe a) -> (a -> m b) -> m ()

   monad-loops	Control.Monad.Loops

   As long as the supplied Maybe expression returns "Just _", the loop body will be called and passed the value contained in the Just. Results are discarded.

8. adjust :: (Eq k, Hashable k) => (v -> v) -> k -> HashMap k v -> HashMap k v

   rio	RIO.HashMap

   Adjust the value tied to a given key in this map only if it is present. Otherwise, leave the map alone.

9. _Just :: forall a a' f . Applicative f => (a -> f a') -> Maybe a -> f (Maybe a')

   rio	RIO.Lens

   _Just targets the value contained in a Maybe, provided it's a Just. See documentation for _Left (as these 2 are pretty similar). In particular, it can be used to write these:

   • Unsafely extracting a value from a Just:

   fromJust = (^?! _Just)
   
   

   • Checking whether a value is a Just:

   isJust = has _Just
   
   

   • Converting a Maybe to a list (empty or consisting of a single element):

   maybeToList = (^.. _Just)
   
   

   • Gathering all Justs in a list:

   catMaybes = (^.. each . _Just)
   
   

10. adjust :: Ord k => (a -> a) -> k -> Map k a -> Map k a

    rio	RIO.Map

    Update a value at a specific key with the result of the provided function. When the key is not a member of the map, the original map is returned.

    adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
    adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
    adjust ("new " ++) 7 empty                         == empty
    

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