Control.Applicative.Lift

Adding a new kind of pure computation to an applicative functor.

Lifting an applicative

data Lift f a

Applicative functor formed by adding pure computations to a given applicative functor.

Constructors

Pure a

Other (f a)

Instances

Functor f => Functor (Lift f)

Methods

fmap :: (a -> b) -> Lift f a -> Lift f b

(<$) :: a -> Lift f b -> Lift f a

Applicative f => Applicative (Lift f)

A combination is Pure only if both parts are.

Methods

pure :: a -> Lift f a

(<*>) :: Lift f (a -> b) -> Lift f a -> Lift f b

(*>) :: Lift f a -> Lift f b -> Lift f b

(<*) :: Lift f a -> Lift f b -> Lift f a

Foldable f => Foldable (Lift f)

Methods

fold :: Monoid m => Lift f m -> m

foldMap :: Monoid m => (a -> m) -> Lift f a -> m

foldr :: (a -> b -> b) -> b -> Lift f a -> b

foldr' :: (a -> b -> b) -> b -> Lift f a -> b

foldl :: (b -> a -> b) -> b -> Lift f a -> b

foldl' :: (b -> a -> b) -> b -> Lift f a -> b

foldr1 :: (a -> a -> a) -> Lift f a -> a

foldl1 :: (a -> a -> a) -> Lift f a -> a

toList :: Lift f a -> [a]

null :: Lift f a -> Bool

length :: Lift f a -> Int

elem :: Eq a => a -> Lift f a -> Bool

maximum :: Ord a => Lift f a -> a

minimum :: Ord a => Lift f a -> a

sum :: Num a => Lift f a -> a

product :: Num a => Lift f a -> a

Traversable f => Traversable (Lift f)

Methods

traverse :: Applicative f => (a -> f b) -> Lift f a -> f (Lift f b)

sequenceA :: Applicative f => Lift f (f a) -> f (Lift f a)

mapM :: Monad m => (a -> m b) -> Lift f a -> m (Lift f b)

sequence :: Monad m => Lift f (m a) -> m (Lift f a)

Eq1 f => Eq1 (Lift f)

Methods

liftEq :: (a -> b -> Bool) -> Lift f a -> Lift f b -> Bool

Ord1 f => Ord1 (Lift f)

Methods

liftCompare :: (a -> b -> Ordering) -> Lift f a -> Lift f b -> Ordering

Read1 f => Read1 (Lift f)

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Lift f a)

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Lift f a]

Show1 f => Show1 (Lift f)

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Lift f a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Lift f a] -> ShowS

Alternative f => Alternative (Lift f)

A combination is Pure only either part is.

Methods

empty :: Lift f a

(<|>) :: Lift f a -> Lift f a -> Lift f a

some :: Lift f a -> Lift f [a]

many :: Lift f a -> Lift f [a]

(Eq1 f, Eq a) => Eq (Lift f a)

Methods

(==) :: Lift f a -> Lift f a -> Bool

(/=) :: Lift f a -> Lift f a -> Bool

(Ord1 f, Ord a) => Ord (Lift f a)

Methods

compare :: Lift f a -> Lift f a -> Ordering

(<) :: Lift f a -> Lift f a -> Bool

(<=) :: Lift f a -> Lift f a -> Bool

(>) :: Lift f a -> Lift f a -> Bool

(>=) :: Lift f a -> Lift f a -> Bool

max :: Lift f a -> Lift f a -> Lift f a

min :: Lift f a -> Lift f a -> Lift f a

(Read1 f, Read a) => Read (Lift f a)

Methods

readsPrec :: Int -> ReadS (Lift f a)

readList :: ReadS [Lift f a]

readPrec :: ReadPrec (Lift f a)

readListPrec :: ReadPrec [Lift f a]

(Show1 f, Show a) => Show (Lift f a)

Methods

showsPrec :: Int -> Lift f a -> ShowS

show :: Lift f a -> String

showList :: [Lift f a] -> ShowS

unLift :: Applicative f => Lift f a -> f a

Projection to the other functor.

mapLift :: (f a -> g a) -> Lift f a -> Lift g a

Apply a transformation to the other computation.

elimLift :: (a -> r) -> (f a -> r) -> Lift f a -> r

Eliminator for Lift.

• elimLift f g . pure = f

• elimLift f g . Other = g

Collecting errors

type Errors e = Lift (Constant e)

An applicative functor that collects a monoid (e.g. lists) of errors. A sequence of computations fails if any of its components do, but unlike monads made with ExceptT from Control.Monad.Trans.Except, these computations continue after an error, collecting all the errors.

• pure f <*> pure x = pure (f x)

• pure f <*> failure e = failure e

• failure e <*> pure x = failure e

• failure e1 <*> failure e2 = failure (e1 <> e2)

runErrors :: Errors e a -> Either e a

Extractor for computations with accumulating errors.

• runErrors (pure x) = Right x

• runErrors (failure e) = Left e

failure :: e -> Errors e a

Report an error.

eitherToErrors :: Either e a -> Errors e a

Convert from Either to Errors (inverse of runErrors).