Safe Haskell	None
Language	Haskell2010

Distribution.Compat.Lens

Contents

Types
- LensLike
- rank-1 types
Getter
Setter
Fold
Lens
Common lenses
Operators
Internal Comonads
Cabal developer info

Description

This module provides very basic lens functionality, without extra dependencies.

For the documentation of the combinators see lens package. This module uses the same vocabulary.

Synopsis

type Lens s t a b = forall f. Functor f => LensLike f s t a b
type Lens' s a = Lens s s a a
type Traversal s t a b = forall f. Applicative f => LensLike f s t a b
type Traversal' s a = Traversal s s a a
type LensLike f s t a b = (a -> f b) -> s -> f t
type LensLike' f s a = (a -> f a) -> s -> f s
type Getting r s a = LensLike (Const r) s s a a
type AGetter s a = LensLike (Const a) s s a a
type ASetter s t a b = LensLike Identity s t a b
type ALens s t a b = LensLike (Pretext a b) s t a b
type ALens' s a = ALens s s a a
view :: Getting a s a -> s -> a
use :: MonadState s m => Getting a s a -> m a
getting :: (s -> a) -> Getting r s a
set :: ASetter s t a b -> b -> s -> t
over :: ASetter s t a b -> (a -> b) -> s -> t
toDListOf :: Getting (DList a) s a -> s -> DList a
toListOf :: Getting (DList a) s a -> s -> [a]
toSetOf :: Getting (Set a) s a -> s -> Set a
cloneLens :: Functor f => ALens s t a b -> LensLike f s t a b
aview :: ALens s t a b -> s -> a
_1 :: Lens (a, c) (b, c) a b
_2 :: Lens (c, a) (c, b) a b
(&) :: a -> (a -> b) -> b
(^.) :: s -> Getting a s a -> a
(.~) :: ASetter s t a b -> b -> s -> t
(?~) :: ASetter s t a (Maybe b) -> b -> s -> t
(%~) :: ASetter s t a b -> (a -> b) -> s -> t
(.=) :: MonadState s m => ASetter s s a b -> b -> m ()
(?=) :: MonadState s m => ASetter s s a (Maybe b) -> b -> m ()
(%=) :: MonadState s m => ASetter s s a b -> (a -> b) -> m ()
(^#) :: s -> ALens s t a b -> a
(#~) :: ALens s t a b -> b -> s -> t
(#%~) :: ALens s t a b -> (a -> b) -> s -> t
data Pretext a b t = Pretext {
- runPretext :: forall f. Functor f => (a -> f b) -> f t
}

Types

type Lens s t a b = forall f. Functor f => LensLike f s t a b Source #

type Lens' s a = Lens s s a a Source #

type Traversal s t a b = forall f. Applicative f => LensLike f s t a b Source #

type Traversal' s a = Traversal s s a a Source #

LensLike

type LensLike f s t a b = (a -> f b) -> s -> f t Source #

type LensLike' f s a = (a -> f a) -> s -> f s Source #

rank-1 types

type Getting r s a = LensLike (Const r) s s a a Source #

type AGetter s a = LensLike (Const a) s s a a Source #

type ASetter s t a b = LensLike Identity s t a b Source #

type ALens s t a b = LensLike (Pretext a b) s t a b Source #

type ALens' s a = ALens s s a a Source #

Getter

view :: Getting a s a -> s -> a Source #

use :: MonadState s m => Getting a s a -> m a Source #

getting :: (s -> a) -> Getting r s a Source #

>>> (3 :: Int) ^. getting (+2) . getting show
"5"

Since: Cabal-2.4

Setter

set :: ASetter s t a b -> b -> s -> t Source #

over :: ASetter s t a b -> (a -> b) -> s -> t Source #

Fold

toDListOf :: Getting (DList a) s a -> s -> DList a Source #

toListOf :: Getting (DList a) s a -> s -> [a] Source #

toSetOf :: Getting (Set a) s a -> s -> Set a Source #

Lens

cloneLens :: Functor f => ALens s t a b -> LensLike f s t a b Source #

aview :: ALens s t a b -> s -> a Source #

Common lenses

_1 :: Lens (a, c) (b, c) a b Source #

_2 :: Lens (c, a) (c, b) a b Source #

Operators

(&) :: a -> (a -> b) -> b infixl 1 Source #

& is a reverse application operator

(^.) :: s -> Getting a s a -> a infixl 8 Source #

(.~) :: ASetter s t a b -> b -> s -> t infixr 4 Source #

(?~) :: ASetter s t a (Maybe b) -> b -> s -> t infixr 4 Source #

(%~) :: ASetter s t a b -> (a -> b) -> s -> t infixr 4 Source #

(.=) :: MonadState s m => ASetter s s a b -> b -> m () infixr 4 Source #

(?=) :: MonadState s m => ASetter s s a (Maybe b) -> b -> m () infixr 4 Source #

(%=) :: MonadState s m => ASetter s s a b -> (a -> b) -> m () infixr 4 Source #

(^#) :: s -> ALens s t a b -> a infixl 8 Source #

(#~) :: ALens s t a b -> b -> s -> t infixr 4 Source #

(#%~) :: ALens s t a b -> (a -> b) -> s -> t infixr 4 Source #

Internal Comonads

data Pretext a b t Source #

lens variant is also parametrised by profunctor.

Constructors

Pretext
Fields runPretext :: forall f. Functor f => (a -> f b) -> f t

Instances

Instances details

Functor (Pretext a b) #
Instance details Defined in Distribution.Compat.Lens Methods fmap :: (a0 -> b0) -> Pretext a b a0 -> Pretext a b b0 Source # (<$) :: a0 -> Pretext a b b0 -> Pretext a b a0 Source #

Cabal developer info

We cannot depend on template-haskell, because Cabal is a boot library. This fact makes defining optics a manual task. Here is a small recipe to make the process less tedious.

First start a repl

cabal new-repl Cabal:hackage-tests

Because --extra-package isn't yet implemented, we use a test-suite with generics-sop dependency.

In the repl, we load a helper script:

:l ../generics-sop-lens.hs

Now we are set up to derive lenses!

:m +Distribution.Types.SourceRepo
putStr $ genericLenses (Proxy :: Proxy SourceRepo)

repoKind :: Lens' SourceRepo RepoKind
repoKind f s = fmap (\x -> s { T.repoKind = x }) (f (T.repoKind s))
{-# INLINE repoKind #-}
...

Note: You may need to adjust type-aliases, e.g. String to FilePath.