# barbies-layered

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This is like [barbies](https://hackage.haskell.org/package/barbies) but these clothes are layered.

For example when there is a following data type,

```haskell
data Foo = Foo { foo :: [Int] }
```

barbies requires a following.

```haskell
data Foo f = Foo { foo :: f [Int] }
```

But in case of barbies-layered,

```haskell
data Foo f = Foo { foo :: f [f Int] }
```

A typical difference is a type of `bmap`.

```haskell
-- barbies
type FunctorB :: ((k -> Type) -> Type) -> Constraint
class FunctorB b where
  bmap :: (forall a. f a -> g a) -> b f -> b g

-- barbies-layered
type FunctorB :: ((Type -> Type) -> Type) -> Constraint
class FunctorB b where
  bmap :: (Functor f, Functor g) => (forall a. f a -> g a) -> b f -> b g
```