Control.Lens.Internal.PrismTH

Documentation

makePrisms

Arguments

:: Name

Type constructor name

-> DecsQ

Generate a Prism for each constructor of a data type. Isos generated when possible. Reviews are created for constructors with existentially quantified constructors and GADTs.

e.g.

data FooBarBaz a
  = Foo Int
  | Bar a
  | Baz Int Char
makePrisms ''FooBarBaz

will create

_Foo :: Prism' (FooBarBaz a) Int
_Bar :: Prism (FooBarBaz a) (FooBarBaz b) a b
_Baz :: Prism' (FooBarBaz a) (Int, Char)

makeClassyPrisms

Arguments

:: Name

Type constructor name

-> DecsQ

Generate a Prism for each constructor of a data type and combine them into a single class. No Isos are created. Reviews are created for constructors with existentially quantified constructors and GADTs.

e.g.

data FooBarBaz a
  = Foo Int
  | Bar a
  | Baz Int Char
makeClassyPrisms ''FooBarBaz

will create

class AsFooBarBaz s a | s -> a where
  _FooBarBaz :: Prism' s (FooBarBaz a)
  _Foo :: Prism' s Int
  _Bar :: Prism' s a
  _Baz :: Prism' s (Int,Char)

  _Foo = _FooBarBaz . _Foo
  _Bar = _FooBarBaz . _Bar
  _Baz = _FooBarBaz . _Baz

instance AsFooBarBaz (FooBarBaz a) a

Generate an As class of prisms. Names are selected by prefixing the constructor name with an underscore. Constructors with multiple fields will construct Prisms to tuples of those fields.

In the event that the name of a data type is also the name of one of its constructors, the name of the Prism generated for the data type will be prefixed with an extra _ (if the data type name is prefix) or . (if the name is infix) to disambiguate it from the Prism for the corresponding constructor. For example, this code:

data Quux = Quux Int | Fred Bool
makeClassyPrisms ''Quux

will create:

class AsQuux s where
  __Quux :: Prism' s Quux -- Data type prism
  _Quux :: Prism' s Int   -- Constructor prism
  _Fred :: Prism' s Bool

  _Quux = __Quux . _Quux
  _Fred = __Quux . _Fred

instance AsQuux Quux

makeDecPrisms

Arguments

:: Bool

generate top-level definitions

-> Dec

-> DecsQ

Generate prisms for the given Dec