transformers-0.5.2.0: Concrete functor and monad transformers

Copyright | (c) Ross Paterson 2010
License | BSD-style (see the file LICENSE)
Maintainer | R.Paterson@city.ac.uk
Stability | experimental
Portability | portable
Safe Haskell | Safe
Language | Haskell98

Control.Applicative.Lift

Contents

- Lifting an applicative
- Collecting errors

Description

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

Synopsis

- data Lift f a
  - = Pure a
  - | Other (f a)
- unLift :: Applicative f => Lift f a -> f a
- mapLift :: (f a -> g a) -> Lift f a -> Lift g a
- type Errors e = Lift (Constant e)
- runErrors :: Errors e a -> Either e a
- failure :: e -> Errors e a

# 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 Source # (<$) :: a -> Lift f b -> Lift f a Source #
Applicative f => Applicative (Lift f) # | A combination is `Pure` only if both parts are.
Methods pure :: a -> Lift f a Source # (<*>) :: Lift f (a -> b) -> Lift f a -> Lift f b Source # liftA2 :: (a -> b -> c) -> Lift f a -> Lift f b -> Lift f c Source # (*>) :: Lift f a -> Lift f b -> Lift f b Source # (<*) :: Lift f a -> Lift f b -> Lift f a Source #
Foldable f => Foldable (Lift f) # |

Methods

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

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

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

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

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

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

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

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

toList :: Lift f a -> [a] Source #

null :: Lift f a -> Bool Source #

length :: Lift f a -> Int Source #

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

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

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

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

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

Traversable f => Traversable (Lift f) # |
Methods traverse :: Applicative f => (a -> f b) -> Lift f a -> f (Lift f b) Source # sequenceA :: Applicative f => Lift f (f a) -> f (Lift f a) Source # mapM :: Monad m => (a -> m b) -> Lift f a -> m (Lift f b) Source # sequence :: Monad m => Lift f (m a) -> m (Lift f a) Source #
Eq1 f => Eq1 (Lift f) # |
Methods liftEq :: (a -> b -> Bool) -> Lift f a -> Lift f b -> Bool Source #
Ord1 f => Ord1 (Lift f) # |
Methods liftCompare :: (a -> b -> Ordering) -> Lift f a -> Lift f b -> Ordering Source #
Read1 f => Read1 (Lift f) # |
Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Lift f a) Source # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Lift f a] Source # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Lift f a) Source # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Lift f a] Source #
Show1 f => Show1 (Lift f) # |
Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Lift f a -> ShowS Source # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Lift f a] -> ShowS Source #
Alternative f => Alternative (Lift f) # | A combination is `Pure` only either part is.
Methods empty :: Lift f a Source # (<|>) :: Lift f a -> Lift f a -> Lift f a Source # some :: Lift f a -> Lift f [a] Source # many :: Lift f a -> Lift f [a] Source #
(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) Source # readList :: ReadS [Lift f a] Source # readPrec :: ReadPrec (Lift f a) Source # readListPrec :: ReadPrec [Lift f a] Source #
(Show1 f, Show a) => Show (Lift f a) # |
Methods showsPrec :: Int -> Lift f a -> ShowS Source # show :: Lift f a -> String Source # showList :: [Lift f a] -> ShowS Source #

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.

# 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.