| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Mini.Lens
Description
Minimal library of van Laarhoven lenses: composable polymorphic record updates
Types
type Lens s t a b = forall f. Functor f => (a -> f b) -> s -> f t Source #
A purely functional reference for updating structures of type s with fields of type a to structures of type t with fields of type b
Construction
lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b Source #
From a getter and a setter to a lens
data Foo = Foo { _bar :: Bar } deriving Show
data Bar = Bar { _baz :: Int } deriving Show
bar :: Lens Foo Foo Bar Bar
bar = lens _bar $ \s b -> s { _bar = b }
baz :: Lens Bar Bar Int Int
baz = lens _baz $ \s b -> s { _baz = b }Reading
view :: Lens s t a b -> s -> a Source #
From a lens and a structure to the value of the field of the structure referenced by the lens
ghci> view (bar . baz) $ Foo (Bar 73) 73
Modifying
over :: Lens s t a b -> (a -> b) -> s -> t Source #
From a lens, an operation and a structure to the structure updated by applying the operation to the value of the field referenced by the lens
ghci> over (bar . baz) (+ 1) $ Foo (Bar 73)
Foo {_bar = Bar {_baz = 74}}