5f262ef · generic-lens

README.md+6−6

compare with master

unifiedsplit

@@ -75,7 +75,7 @@ True

75

76## Structural subtyping

77

78−A record is a (structural) `subtype' of another, if its fields are a subset of

78+A record is a (structural) `subtype' of another, if its fields are a superset of

79those of the other.

80

81```haskell

@@ -103,18 +103,18 @@ Animal {name = "Tunyasz", age = 50}

103>>> smash (Animal "dog" 10) human

104Human {name = "dog", age = 10, address = "London"}

105

106−-- 'subtype' is a lens that focuses on a subrecord of a larger record:

106+-- 'super' is a lens that focuses on a subrecord of a larger record:

107−>>> human ^. subtype @Animal

107+>>> human ^. super @Animal

108Animal {name = "Tunyasz", age = 50}

109```

110

111−We can apply a function that operates on a subtype to the larger structure,

111+We can apply a function that operates on a supertype to the larger (subtype)

112−by focusing on the subtype first:

112+structure, by focusing on the supertype first:

113

114```haskell

115growUp :: Animal -> Animal

116growUp (Animal name age) = Animal name (age + 50)

117

118−>>> human & subtype @Animal %~ growUp

118+>>> human & super @Animal %~ growUp

119Human {name = "Tunyasz", age = 60, address = "London"}

120```

generic-lens.cabal+2

@@ -53,6 +53,8 @@ library

53

54 -- Other library packages from which modules are imported.

55 build-depends: base >= 4.9 && <= 5.0

56+ , lens

57+ , kan-extensions

56

58

57 -- Directories containing source files.

59 -- Directories containing source files.

58 hs-source-dirs: src

60 hs-source-dirs: src

src/Data/Generics/Internal/Lens.hs+1

@@ -34,6 +34,7 @@ type Lens' s a

34-- | Getting

35(^.) :: s -> ((a -> Const a a) -> s -> Const a s) -> a

36s ^. l = getConst (l Const s)

37+infixl 8 ^.

37

38

38-- | Setting

39-- | Setting

39set :: ((a -> Identity b) -> s -> Identity t) -> b -> s -> t

40set :: ((a -> Identity b) -> s -> Identity t) -> b -> s -> t

src/Data/Generics/Record.hs+1−1

@@ -18,7 +18,7 @@ module Data.Generics.Record

18 (

19 -- * Subtype relationship

20 Subtype (..)

21− , subtype

21+ , super

22

23 -- * Magic lens

24 , HasField (..)

src/Data/Generics/Record/Subtype.hs+5−5

@@ -49,7 +49,7 @@

49-----------------------------------------------------------------------------

50module Data.Generics.Record.Subtype

51 ( Subtype (..)

52− , subtype

52+ , super

53 ) where

54

55import Data.Generics.Record.HasField

@@ -86,13 +86,13 @@ instance (GSmash (Rep a) (Rep b), GUpcast (Rep a) (Rep b), Generic a, Generic b)

86-- | Structural subtype lens. Given a subtype relationship @sub :< sup@,

87-- we can focus on the @sub@ structure of @sup@.

88--

89−-- >>> human ^. subtype @Animal

89+-- >>> human ^. super @Animal

90-- Animal {name = "Tunyasz", age = 50}

91--

92−-- >>> set (subtype @Animal) (Animal "dog" 10) human

92+-- >>> set (super @Animal) (Animal "dog" 10) human

93-- Human {name = "dog", age = 10, address = "London"}

94−subtype :: forall sup sub. Subtype sub sup => Lens' sub sup

94+super :: forall sup sub. Subtype sub sup => Lens' sub sup

95−subtype f sub = fmap (flip smash sub) (f (upcast sub))

95+super f sub = fmap (flip smash sub) (f (upcast sub))

96

97--------------------------------------------------------------------------------

98-- * Generic upcasting