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Within LTS Haskell 24.65 (ghc-9.10.3)
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whenMaybe :: Applicative m => Bool -> m a -> m (Maybe a)extra Extra Like when, but return either Nothing if the predicate was False, or Just with the result of the computation.
whenMaybe True (print 1) == fmap Just (print 1) whenMaybe False (print 1) == pure Nothing
whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a)extra Extra Like whenMaybe, but where the test can be monadic.
runMaybeApply :: MaybeApply (f :: Type -> Type) a -> Either (f a) asemigroupoids Data.Functor.Apply No documentation available.
runMaybeApply :: MaybeApply (f :: Type -> Type) a -> Either (f a) asemigroupoids Data.Functor.Bind No documentation available.
runMaybeApply :: MaybeApply (f :: Type -> Type) a -> Either (f a) asemigroupoids Data.Functor.Bind.Class No documentation available.
traverse1Maybe :: (Traversable t, Apply f) => (a -> f b) -> t a -> MaybeApply f (t b)semigroupoids Data.Functor.Bind.Class Traverse a Traversable using Apply, getting the results back in a MaybeApply.
traverse1Maybe :: (Traversable t, Apply f) => (a -> f b) -> t a -> MaybeApply f (t b)semigroupoids Data.Semigroup.Traversable Traverse a Traversable using Apply, getting the results back in a MaybeApply.
minusNaturalMaybe :: Natural -> Natural -> Maybe Naturalbase-compat Numeric.Natural.Compat Natural subtraction. Returns Nothings for non-positive results.
readMaybe :: Read a => String -> Maybe abase-compat Text.Read.Compat Parse a string using the Read instance. Succeeds if there is exactly one valid result.
>>> readMaybe "123" :: Maybe Int Just 123
>>> readMaybe "hello" :: Maybe Int Nothing
partitionMaybe :: (a -> Maybe b) -> [a] -> ([b], [a])utility-ht Data.List.HT Partition a list into elements which evaluate to Just or Nothing by f.
forAllMaybeFn $ \f xs -> partitionMaybe f xs == (mapMaybe f xs, filter (isNothing . f) xs)
forAllPredicates $ \p xs -> partition p xs == partitionMaybe (\x -> toMaybe (p x) x) xs