Safe Haskell | Safe-Inferred |
---|---|
Language | GHC2021 |
foldMap
for generic data types.
foldMap
can be considered a two-step process:
Applying this to generic data types:
Field mappings are handled using a per-monoid type class. You need a monoid m
with an associated type class which has a function a -> m
. Write a
GenericFoldMap
instance for your monoid which points to your type class. If a
field type doesn't have a matching instance, the generic instance emits a type
error.
Sum types (with multiple constructors) are handled by (<>)
-ing the constructor
with its contents (in that order). You must provide a String -> m
function for
mapping constructor names. If you need custom sum type handling, you may write
your own and still leverage the individual constructor generics.
This function can provide generic support for simple fold-y operations like serialization.
Synopsis
- class GenericFoldMap m where
- type GenericFoldMapC m a :: Constraint
- genericFoldMapF :: GenericFoldMapC m a => a -> m
- genericFoldMapNonSum :: forall m a. (Generic a, GFoldMapNonSum m (Rep a)) => a -> m
- class GFoldMapNonSum m f
- genericFoldMapSum :: forall m a. (Generic a, GFoldMapSum m (Rep a)) => (String -> m) -> a -> m
- class GFoldMapSum m f
Documentation
class GenericFoldMap m where Source #
type GenericFoldMapC m a :: Constraint Source #
The type class that enables mapping permitted types to the monoid.
The type class should provide a function that looks like
genericFoldMapF
.
genericFoldMapF :: GenericFoldMapC m a => a -> m Source #
The "map" function in foldMap
(first argument).
Instances
Monoid m => GenericFoldMap (EmptyRec0 m) Source # | |
Defined in Generic.Data.Function.FoldMap.Constructor type GenericFoldMapC (EmptyRec0 m) a Source # genericFoldMapF :: GenericFoldMapC (EmptyRec0 m) a => a -> EmptyRec0 m Source # | |
GenericFoldMap (NoRec0 m) Source # |
|
Defined in Generic.Data.Function.FoldMap.Constructor type GenericFoldMapC (NoRec0 m) a Source # genericFoldMapF :: GenericFoldMapC (NoRec0 m) a => a -> NoRec0 m Source # |
genericFoldMapNonSum :: forall m a. (Generic a, GFoldMapNonSum m (Rep a)) => a -> m Source #
Generic foldMap
over a term of non-sum data type a
.
a
must have exactly one constructor.
class GFoldMapNonSum m f Source #
foldMap
over generic product data types.
Take a generic representation, map each field in the data type to a Monoid
,
and combine the results with (<>
).
Instances
(TypeError ENoEmpty :: Constraint) => GFoldMapNonSum m (V1 :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.NonSum gFoldMapNonSum :: forall (p :: k0). V1 p -> m Source # | |
(TypeError EUnexpectedSum :: Constraint) => GFoldMapNonSum m (l :+: r :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.NonSum gFoldMapNonSum :: forall (p :: k0). (l :+: r) p -> m Source # | |
GFoldMapC m f => GFoldMapNonSum m (C1 c f :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.NonSum gFoldMapNonSum :: forall (p :: k0). C1 c f p -> m Source # | |
GFoldMapNonSum m f => GFoldMapNonSum m (D1 c f :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.NonSum gFoldMapNonSum :: forall (p :: k0). D1 c f p -> m Source # |
genericFoldMapSum :: forall m a. (Generic a, GFoldMapSum m (Rep a)) => (String -> m) -> a -> m Source #
Generic foldMap
over a term of sum data type a
.
a
must have at least two constructors.
You must provide a function for mapping constructor names to monoidal values.
class GFoldMapSum m f Source #
Instances
(TypeError ENoEmpty :: Constraint) => GFoldMapSum m (V1 :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.Sum gFoldMapSum :: forall (p :: k0). (String -> m) -> V1 p -> m Source # | |
GFoldMapCSum m (l :+: r) => GFoldMapSum m (l :+: r :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.Sum gFoldMapSum :: forall (p :: k0). (String -> m) -> (l :+: r) p -> m Source # | |
(TypeError EUnexpectedNonSum :: Constraint) => GFoldMapSum m (C1 c f :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.Sum gFoldMapSum :: forall (p :: k0). (String -> m) -> C1 c f p -> m Source # | |
GFoldMapSum m f => GFoldMapSum m (D1 c f :: k -> Type) Source # | |
Defined in Generic.Data.Function.FoldMap.Sum gFoldMapSum :: forall (p :: k0). (String -> m) -> D1 c f p -> m Source # |