Copyright | (C) 2020 Csongor Kiss |
---|---|
License | BSD3 |
Maintainer | Csongor Kiss <kiss.csongor.kiss@gmail.com> |
Stability | experimental |
Portability | non-portable |
Safe Haskell | None |
Language | Haskell2010 |
Derive constructor-name-based prisms generically.
Synopsis
- class AsConstructor (ctor :: Symbol ) s t a b | ctor s -> a, ctor t -> b where
- class AsConstructor_ (ctor :: Symbol ) s t a b where
- class AsConstructor' (ctor :: Symbol ) s a | ctor s -> a where
- class AsConstructor0 (ctor :: Symbol ) s t a b where
Prisms
Running example:
>>>
:set -XTypeApplications
>>>
:set -XDataKinds
>>>
:set -XDeriveGeneric
>>>
:set -XFlexibleContexts
>>>
:set -XTypeFamilies
>>>
import GHC.Generics
>>>
import Control.Lens
>>>
:m +Data.Generics.Product.Fields
>>>
:m +Data.Function
>>>
:{
data Animal a = Dog (Dog a) | Cat Name Age | Duck Age deriving (Generic, Show) data Dog a = MkDog { name :: Name , age :: Age , fieldA :: a } deriving Show type Name = String type Age = Int dog, cat, duck :: Animal Int dog = Dog (MkDog "Shep" 3 30) cat = Cat "Mog" 5 duck = Duck 2 :}
class AsConstructor (ctor :: Symbol ) s t a b | ctor s -> a, ctor t -> b where Source #
Sums that have a constructor with a given name.
_Ctor :: Prism s t a b Source #
A prism that projects a named constructor from a sum. Compatible with the
lens package's
Prism
type.
>>>
dog ^? _Ctor @"Dog"
Just (MkDog {name = "Shep", age = 3, fieldA = 30})
>>>
dog ^? _Ctor @"Cat"
Nothing
>>>
cat ^? _Ctor @"Cat"
Just ("Mog",5)
>>>
_Ctor @"Cat" # ("Garfield", 6) :: Animal Int
Cat "Garfield" 6
Type errors
>>>
cat ^? _Ctor @"Turtle"
... ... ... The type Animal Int does not contain a constructor named "Turtle" ...
Instances
( Context ctor s t a b, AsConstructor0 ctor s t a b) => AsConstructor ctor s t a b Source # | |
Defined in Data.Generics.Sum.Constructors |
|
AsConstructor ctor ( Void1 a) ( Void1 b) a b Source # |
See Note [Uncluttering type signatures] >>> :t +d _Ctor _Ctor :: (AsConstructor ctor s t a b, Choice p, Applicative f) => p a (f b) -> p s (f t) |
class AsConstructor_ (ctor :: Symbol ) s t a b where Source #
Sums that have a constructor with a given name.
The difference between
HasConstructor
and
HasConstructor_
is similar to
the one between
HasField
and
HasField_
.
See
HasField_
.
Instances
( Context_ ctor s t a b, AsConstructor0 ctor s t a b) => AsConstructor_ ctor s t a b Source # | |
Defined in Data.Generics.Sum.Constructors |
|
AsConstructor_ ctor ( Void1 a) ( Void1 b) a b Source # | |
class AsConstructor' (ctor :: Symbol ) s a | ctor s -> a where Source #
Instances
( Context' ctor s a, AsConstructor0 ctor s s a a) => AsConstructor' ctor s a Source # | |
Defined in Data.Generics.Sum.Constructors |
class AsConstructor0 (ctor :: Symbol ) s t a b where Source #
Sums that have a constructor with a given name.
This class gives the minimal constraints needed to define this prism.
For common uses, see
HasConstructor
.
Instances
Context0 ctor s t a b => AsConstructor0 ctor s t a b Source # | |
Defined in Data.Generics.Sum.Constructors |