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

Lifting an applicative

data Lift f a Source

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 (>) :: 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
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 Source

Projection to the other functor.

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

Apply a transformation to the other computation.

Collecting errors

type Errors e = Lift (Constant e) Source

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 Source

Extractor for computations with accumulating errors.

```
runErrors (pure x) = Right x
```
```
runErrors (failure e) = Left e
```

failure :: e -> Errors e a Source

Report an error.