Hoogle Search

Within LTS Haskell 24.5 (ghc-9.10.2)

Note that Stackage only displays results for the latest LTS and Nightly snapshot. Learn more.

Exact lookup

1. handleJust :: (HasCallStack, MonadCatch m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a

   exceptions	Control.Monad.Catch

   Flipped catchJust. See Control.Exception's handleJust.

2. tryJust :: (HasCallStack, MonadCatch m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)

   exceptions	Control.Monad.Catch

   A variant of try that takes an exception predicate to select which exceptions are caught. See Control.Exception's tryJust

3. _Just :: forall a b p f . (Choice p, Applicative f) => p a (f b) -> p (Maybe a) (f (Maybe b))

   lens	Control.Lens.Combinators

   This Prism provides a Traversal for tweaking the target of the value of Just in a Maybe.

   >>> over _Just (+1) (Just 2)
   Just 3
   

   Unlike traverse this is a Prism, and so you can use it to inject as well:

   >>> _Just # 5
   Just 5
   

   >>> 5^.re _Just
   Just 5
   

   Interestingly,

   m ^? _Just ≡ m
   

   >>> Just x ^? _Just
   Just x
   

   >>> Nothing ^? _Just
   Nothing
   

4. _Just :: forall a b p f . (Choice p, Applicative f) => p a (f b) -> p (Maybe a) (f (Maybe b))

   lens	Control.Lens.Prism

   This Prism provides a Traversal for tweaking the target of the value of Just in a Maybe.

   >>> over _Just (+1) (Just 2)
   Just 3
   

   Unlike traverse this is a Prism, and so you can use it to inject as well:

   >>> _Just # 5
   Just 5
   

   >>> 5^.re _Just
   Just 5
   

   Interestingly,

   m ^? _Just ≡ m
   

   >>> Just x ^? _Just
   Just x
   

   >>> Nothing ^? _Just
   Nothing
   

5. _Just :: forall a b p f . (Choice p, Applicative f) => p a (f b) -> p (Maybe a) (f (Maybe b))

   gogol-core	Gogol.Prelude

   This Prism provides a Traversal for tweaking the target of the value of Just in a Maybe.

   >>> over _Just (+1) (Just 2)
   Just 3
   

   Unlike traverse this is a Prism, and so you can use it to inject as well:

   >>> _Just # 5
   Just 5
   

   >>> 5^.re _Just
   Just 5
   

   Interestingly,

   m ^? _Just ≡ m
   

   >>> Just x ^? _Just
   Just x
   

   >>> Nothing ^? _Just
   Nothing
   

6. catchJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> m a -> (b -> m a) -> m a

   unliftio	UnliftIO.Exception

   catchJust is like catch but it takes an extra argument which is an exception predicate, a function which selects which type of exceptions we're interested in.

7. handleJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a

   unliftio	UnliftIO.Exception

   Flipped catchJust.

8. tryJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)

   unliftio	UnliftIO.Exception

   A variant of try that takes an exception predicate to select which exceptions are caught.

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

   microlens	Lens.Micro

   _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. elemIndexJust :: (Partial, Eq a) => a -> [a] -> Int

    safe	Safe

    elemIndexJust op = fromJust . elemIndex op
    

Page 29 of many | Previous | Next