-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | A GHC.Generics based entity component system.
--   
--   Ecstasy is an entity-component system for Haskell. It's inspired by
--   <a>apecs</a>, but makes the design decision to focus on being
--   idiomatic rather than being fast. Maybe. I haven't actually
--   benchmarked it.
--   
--   We achieve being idiomatic by using <a>GHC.Generics</a> and tricky
--   type families to derive performant data stores given only a record of
--   the desired components.
@package ecstasy
@version 0.2.0.1

module Data.Ecstasy.Types

-- | The key for an entity.
newtype Ent
Ent :: Int -> Ent
[unEnt] :: Ent -> Int

-- | The internal state of the <a>SystemT</a> monad.
type SystemState w m = (Int, w ( 'WorldOf m))

-- | A monad transformer over an ECS given a world <tt>w</tt>.
newtype SystemT w m a
SystemT :: StateT (SystemState w m) m a -> SystemT w m a
[runSystemT'] :: SystemT w m a -> StateT (SystemState w m) m a

-- | A monad over an ECS given a world <tt>w</tt>.
type System w = SystemT w Identity

-- | A computation to run over a particular entity.
newtype QueryT w m a
QueryT :: ReaderT (Ent, w  'FieldOf) (MaybeT m) a -> QueryT w m a
[runQueryT'] :: QueryT w m a -> ReaderT (Ent, w  'FieldOf) (MaybeT m) a

-- | A collection of methods necessary to dispatch reads and writes to a
--   <a>Virtual</a> component.
data VTable m a
VTable :: !(Ent -> m (Maybe a)) -> !(Ent -> Update a -> m ()) -> VTable m a

-- | Get the value of an entity's component.
[vget] :: VTable m a -> !(Ent -> m (Maybe a))

-- | Update the value of an entity's component.
[vset] :: VTable m a -> !(Ent -> Update a -> m ())

-- | Data kind used to parameterize the ECS record.
data StorageType

-- | Used to describe the actual entity.
FieldOf :: StorageType

-- | Used to construct the world's storage.
WorldOf :: (Type -> Type) -> StorageType

-- | Used to construct a setter to update an entity.
SetterOf :: StorageType

-- | Data kind used to parameterize the fields of the ECS record.
data ComponentType

-- | This component can be owned by any entity.
Field :: ComponentType

-- | This component can be owned by only a single entity at a time.
Unique :: ComponentType

-- | This component is owned by another system.
Virtual :: ComponentType

-- | Describes how we can change an <tt>a</tt>.
data Update a

-- | Keep the current value.
Keep :: Update a

-- | Delete the current value if it exists.
Unset :: Update a

-- | Set the current value.
Set :: !a -> Update a

-- | A type family to be used in your ECS recrod.
instance Data.Traversable.Traversable Data.Ecstasy.Types.Update
instance Data.Foldable.Foldable Data.Ecstasy.Types.Update
instance GHC.Base.Functor Data.Ecstasy.Types.Update
instance GHC.Read.Read a => GHC.Read.Read (Data.Ecstasy.Types.Update a)
instance GHC.Show.Show a => GHC.Show.Show (Data.Ecstasy.Types.Update a)
instance GHC.Classes.Ord a => GHC.Classes.Ord (Data.Ecstasy.Types.Update a)
instance GHC.Classes.Eq a => GHC.Classes.Eq (Data.Ecstasy.Types.Update a)
instance Control.Monad.IO.Class.MonadIO m => Control.Monad.IO.Class.MonadIO (Data.Ecstasy.Types.SystemT w m)
instance Control.Monad.Writer.Class.MonadWriter ww m => Control.Monad.Writer.Class.MonadWriter ww (Data.Ecstasy.Types.SystemT w m)
instance Control.Monad.Reader.Class.MonadReader r m => Control.Monad.Reader.Class.MonadReader r (Data.Ecstasy.Types.SystemT w m)
instance GHC.Base.Monad m => GHC.Base.Monad (Data.Ecstasy.Types.SystemT w m)
instance GHC.Base.Monad m => GHC.Base.Applicative (Data.Ecstasy.Types.SystemT w m)
instance GHC.Base.Functor m => GHC.Base.Functor (Data.Ecstasy.Types.SystemT w m)
instance GHC.Base.Monad m => GHC.Base.MonadPlus (Data.Ecstasy.Types.QueryT w m)
instance GHC.Base.Monad m => GHC.Base.Alternative (Data.Ecstasy.Types.QueryT w m)
instance Control.Monad.IO.Class.MonadIO m => Control.Monad.IO.Class.MonadIO (Data.Ecstasy.Types.QueryT w m)
instance Control.Monad.Writer.Class.MonadWriter ww m => Control.Monad.Writer.Class.MonadWriter ww (Data.Ecstasy.Types.QueryT w m)
instance Control.Monad.State.Class.MonadState s m => Control.Monad.State.Class.MonadState s (Data.Ecstasy.Types.QueryT w m)
instance GHC.Base.Monad m => GHC.Base.Monad (Data.Ecstasy.Types.QueryT w m)
instance GHC.Base.Monad m => GHC.Base.Applicative (Data.Ecstasy.Types.QueryT w m)
instance GHC.Base.Functor m => GHC.Base.Functor (Data.Ecstasy.Types.QueryT w m)
instance GHC.Classes.Ord Data.Ecstasy.Types.Ent
instance GHC.Classes.Eq Data.Ecstasy.Types.Ent
instance Control.Monad.Trans.Class.MonadTrans (Data.Ecstasy.Types.SystemT w)
instance Control.Monad.State.Class.MonadState s m => Control.Monad.State.Class.MonadState s (Data.Ecstasy.Types.SystemT w m)
instance Control.Monad.Trans.Class.MonadTrans (Data.Ecstasy.Types.QueryT w)
instance Control.Monad.Reader.Class.MonadReader r m => Control.Monad.Reader.Class.MonadReader r (Data.Ecstasy.Types.QueryT w m)
instance GHC.Show.Show Data.Ecstasy.Types.Ent

module Data.Ecstasy.Internal.Deriving
class GConvertSetter a b
gConvertSetter :: GConvertSetter a b => a x -> b x
class GGetEntity m a b
gGetEntity :: GGetEntity m a b => a x -> Int -> m (b x)
class GSetEntity m a b
gSetEntity :: GSetEntity m a b => a x -> Int -> b x -> m (b x)
def :: forall keep a. (Generic a, GDefault keep (Rep a)) => a
class GDefault (keep :: Bool) f
gdef :: GDefault keep f => f a
instance Data.Ecstasy.Internal.Deriving.GDefault keep GHC.Generics.U1
instance Data.Ecstasy.Internal.Deriving.GDefault keep (GHC.Generics.K1 i (GHC.Base.Maybe c))
instance Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.False (GHC.Generics.K1 i (Data.Ecstasy.Types.Update c))
instance Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.K1 i (Data.Ecstasy.Types.Update c))
instance Data.Ecstasy.Internal.Deriving.GDefault keep (GHC.Generics.K1 i (Data.IntMap.Internal.IntMap c))
instance (GHC.Base.Applicative m, GHC.TypeLits.KnownSymbol sym) => Data.Ecstasy.Internal.Deriving.GDefault keep (GHC.Generics.M1 GHC.Generics.S ('GHC.Generics.MetaSel ('GHC.Base.Just sym) x y z) (GHC.Generics.K1 i (Data.Ecstasy.Types.VTable m a)))
instance Data.Ecstasy.Internal.Deriving.GDefault keep f => Data.Ecstasy.Internal.Deriving.GDefault keep (GHC.Generics.M1 i c f)
instance (Data.Ecstasy.Internal.Deriving.GDefault keep a, Data.Ecstasy.Internal.Deriving.GDefault keep b) => Data.Ecstasy.Internal.Deriving.GDefault keep (a GHC.Generics.:*: b)
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GSetEntity m (GHC.Generics.K1 i (Data.Ecstasy.Types.Update a)) (GHC.Generics.K1 i' (GHC.Base.Maybe (GHC.Types.Int, a)))
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GSetEntity m (GHC.Generics.K1 i (Data.Ecstasy.Types.Update a)) (GHC.Generics.K1 i' (Data.Ecstasy.Types.VTable m a))
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GSetEntity m (GHC.Generics.K1 i (Data.Ecstasy.Types.Update a)) (GHC.Generics.K1 i' (Data.IntMap.Internal.IntMap a))
instance (GHC.Base.Functor m, Data.Ecstasy.Internal.Deriving.GSetEntity m f f') => Data.Ecstasy.Internal.Deriving.GSetEntity m (GHC.Generics.M1 i c f) (GHC.Generics.M1 i' c' f')
instance (GHC.Base.Applicative m, Data.Ecstasy.Internal.Deriving.GSetEntity m a c, Data.Ecstasy.Internal.Deriving.GSetEntity m b d) => Data.Ecstasy.Internal.Deriving.GSetEntity m (a GHC.Generics.:*: b) (c GHC.Generics.:*: d)
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GGetEntity m (GHC.Generics.K1 i (Data.Ecstasy.Types.VTable m a)) (GHC.Generics.K1 i' (GHC.Base.Maybe a))
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GGetEntity m (GHC.Generics.K1 i (Data.IntMap.Internal.IntMap a)) (GHC.Generics.K1 i' (GHC.Base.Maybe a))
instance GHC.Base.Applicative m => Data.Ecstasy.Internal.Deriving.GGetEntity m (GHC.Generics.K1 i (GHC.Base.Maybe (GHC.Types.Int, a))) (GHC.Generics.K1 i' (GHC.Base.Maybe a))
instance (GHC.Base.Functor m, Data.Ecstasy.Internal.Deriving.GGetEntity m f f') => Data.Ecstasy.Internal.Deriving.GGetEntity m (GHC.Generics.M1 i c f) (GHC.Generics.M1 i' c' f')
instance (GHC.Base.Applicative m, Data.Ecstasy.Internal.Deriving.GGetEntity m a c, Data.Ecstasy.Internal.Deriving.GGetEntity m b d) => Data.Ecstasy.Internal.Deriving.GGetEntity m (a GHC.Generics.:*: b) (c GHC.Generics.:*: d)
instance Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.K1 i a) (GHC.Generics.K1 i' (GHC.Base.Maybe a))
instance Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.K1 i a) (GHC.Generics.K1 i' (Data.Ecstasy.Types.Update a))
instance Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.K1 i (GHC.Base.Maybe a)) (GHC.Generics.K1 i' (Data.Ecstasy.Types.Update a))
instance Data.Ecstasy.Internal.Deriving.GConvertSetter f f' => Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.M1 i c f) (GHC.Generics.M1 i' c' f')
instance (Data.Ecstasy.Internal.Deriving.GConvertSetter a c, Data.Ecstasy.Internal.Deriving.GConvertSetter b d) => Data.Ecstasy.Internal.Deriving.GConvertSetter (a GHC.Generics.:*: b) (c GHC.Generics.:*: d)

module Data.Ecstasy.Internal

-- | This class provides all of the functionality necessary to manipulate
--   the ECS.
class HasWorld' world => HasWorld world m

-- | Fetches an entity from the world given its <a>Ent</a>.
getEntity :: (HasWorld world m, Monad m) => Ent -> SystemT world m (world  'FieldOf)

-- | Fetches an entity from the world given its <a>Ent</a>.
getEntity :: (HasWorld world m, Monad m, GGetEntity m (Rep (world ( 'WorldOf m))) (Rep (world  'FieldOf)), Generic (world  'FieldOf), Generic (world ( 'WorldOf m))) => Ent -> SystemT world m (world  'FieldOf)

-- | Updates an <a>Ent</a> in the world given its setter.
setEntity :: HasWorld world m => Ent -> world  'SetterOf -> SystemT world m ()

-- | Updates an <a>Ent</a> in the world given its setter.
setEntity :: (HasWorld world m, GSetEntity m (Rep (world  'SetterOf)) (Rep (world ( 'WorldOf m))), Generic (world ( 'WorldOf m)), Generic (world  'SetterOf), Monad m) => Ent -> world  'SetterOf -> SystemT world m ()

-- | The default world, which contains only empty containers.
defStorage :: HasWorld world m => world ( 'WorldOf m)

-- | The default world, which contains only empty containers.
defStorage :: (HasWorld world m, Generic (world ( 'WorldOf m)), GDefault  'True (Rep (world ( 'WorldOf m)))) => world ( 'WorldOf m)
class HasWorld' world

-- | Transforms an entity into a setter to transform the default entity
--   into the given one. Used by <a>createEntity</a>.
convertSetter :: HasWorld' world => world  'FieldOf -> world  'SetterOf

-- | Transforms an entity into a setter to transform the default entity
--   into the given one. Used by <a>createEntity</a>.
convertSetter :: (HasWorld' world, GConvertSetter (Rep (world  'FieldOf)) (Rep (world  'SetterOf)), Generic (world  'FieldOf), Generic (world  'SetterOf)) => world  'FieldOf -> world  'SetterOf

-- | The default entity, owning no components.
newEntity :: HasWorld' world => world  'FieldOf

-- | The default entity, owning no components.
newEntity :: (HasWorld' world, Generic (world  'FieldOf), GDefault  'True (Rep (world  'FieldOf))) => world  'FieldOf

-- | The default setter, which keeps all components with their previous
--   value.
unchanged :: HasWorld' world => world  'SetterOf

-- | The default setter, which keeps all components with their previous
--   value.
unchanged :: (HasWorld' world, Generic (world  'SetterOf), GDefault  'True (Rep (world  'SetterOf))) => world  'SetterOf

-- | A setter which will delete the entity if its <a>QueryT</a> matches.
delEntity :: HasWorld' world => world  'SetterOf

-- | A setter which will delete the entity if its <a>QueryT</a> matches.
delEntity :: (HasWorld' world, Generic (world  'SetterOf), GDefault  'False (Rep (world  'SetterOf))) => world  'SetterOf

-- | Retrieve a unique <a>Ent</a>.
nextEntity :: Monad m => SystemT a m Ent

-- | Create a new entity.
createEntity :: (HasWorld world m, Monad m) => world  'FieldOf -> SystemT world m Ent

-- | Delete an entity.
deleteEntity :: (HasWorld world m, Monad m) => Ent -> SystemT world m ()

-- | Evaluate a <a>QueryT</a>.
unQueryT :: QueryT world m a -> Ent -> world  'FieldOf -> m (Maybe a)

-- | Map a <a>QueryT</a> transformation over all entites that match it.
emap :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m (world  'SetterOf) -> SystemT world m ()

-- | Collect the results of a monadic computation over every entity
--   matching a <a>QueryT</a>.
efor :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m a -> SystemT world m [a]

-- | Do an <a>emap</a> and an <a>efor</a> at the same time.
eover :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m (a, world  'SetterOf) -> SystemT world m [a]

-- | Run a <a>QueryT</a> over a particular <a>Ent</a>.
runQueryT :: (HasWorld world m, Monad m) => Ent -> QueryT world m a -> SystemT world m (Maybe a)

-- | Provides a resumable <a>SystemT</a>. This is a pretty big hack until I
--   come up with a better formalization for everything.
yieldSystemT :: Monad m => SystemState world m -> SystemT world m a -> m (SystemState world m, a)

-- | Evaluate a <a>SystemT</a>.
runSystemT :: Monad m => world ( 'WorldOf m) -> SystemT world m a -> m a

-- | Evaluate a <a>System</a>.
runSystem :: world ( 'WorldOf Identity) -> System world a -> a

-- | Only evaluate this <a>QueryT</a> for entities which have the given
--   component.
with :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m ()

-- | Only evaluate this <a>QueryT</a> for entities which do not have the
--   given component.
without :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m ()

-- | Get the value of a component, failing the <a>QueryT</a> if it isn't
--   present.
query :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m a

-- | Attempt to get the value of a component.
queryMaybe :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m (Maybe a)

-- | Get the <a>Ent</a> for whom this query is running.
queryEnt :: Monad m => QueryT world m Ent

-- | Query a flag as a <a>Bool</a>.
queryFlag :: Monad m => (world  'FieldOf -> Maybe ()) -> QueryT world m Bool

-- | Perform a query with a default.
queryDef :: Monad m => z -> (world  'FieldOf -> Maybe z) -> QueryT world m z

-- | An <a>EntTarget</a> is a set of <a>Ent</a>s to iterate over.
type EntTarget world m = SystemT world m [Ent]

-- | Iterate over all entities.
allEnts :: Monad m => EntTarget world m

-- | Iterate over some entities.
someEnts :: Monad m => [Ent] -> EntTarget world m

-- | Iterate over an entity.
anEnt :: Monad m => Ent -> EntTarget world m

-- | Turn a <a>Maybe</a> into an <a>Update</a>.
maybeToUpdate :: Maybe a -> Update a
instance (Data.Ecstasy.Internal.HasWorld' world, GHC.Generics.Generic (world 'Data.Ecstasy.Types.SetterOf), GHC.Generics.Generic (world ('Data.Ecstasy.Types.WorldOf m)), GHC.Generics.Generic (world 'Data.Ecstasy.Types.FieldOf), Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.Rep (world 'Data.Ecstasy.Types.FieldOf)) (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.Rep (world 'Data.Ecstasy.Types.FieldOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.False (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.Rep (world ('Data.Ecstasy.Types.WorldOf m))), Data.Ecstasy.Internal.Deriving.GSetEntity m (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)) (GHC.Generics.Rep (world ('Data.Ecstasy.Types.WorldOf m))), Data.Ecstasy.Internal.Deriving.GGetEntity m (GHC.Generics.Rep (world ('Data.Ecstasy.Types.WorldOf m))) (GHC.Generics.Rep (world 'Data.Ecstasy.Types.FieldOf)), GHC.Base.Monad m) => Data.Ecstasy.Internal.HasWorld world m
instance (GHC.Generics.Generic (world 'Data.Ecstasy.Types.SetterOf), GHC.Generics.Generic (world 'Data.Ecstasy.Types.FieldOf), Data.Ecstasy.Internal.Deriving.GConvertSetter (GHC.Generics.Rep (world 'Data.Ecstasy.Types.FieldOf)) (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.Rep (world 'Data.Ecstasy.Types.FieldOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.False (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf)), Data.Ecstasy.Internal.Deriving.GDefault 'GHC.Types.True (GHC.Generics.Rep (world 'Data.Ecstasy.Types.SetterOf))) => Data.Ecstasy.Internal.HasWorld' world


-- | Ecstasy is a library architected around the <a>HKD pattern</a>, the
--   gist of which is to define a "template" type that can be reused for
--   several purposes. Users of ecstasy should define a record type of
--   <a>Component</a>s parameterized over a variable of kind
--   <a>StorageType</a>:
--   
--   <pre>
--   data World s = Entity
--     { position :: <a>Component</a> s '<a>Field</a> (V2 Double)
--     , graphics :: <a>Component</a> s '<a>Field</a> Graphics
--     , isPlayer :: <a>Component</a> s '<a>Unique</a> ()
--     }
--     deriving (<a>Generic</a>)
--   </pre>
--   
--   Ensure that this type have an instance of <a>Generic</a>.
--   
--   For usability, it might be desirable to also define the following type
--   synonym:
--   
--   <pre>
--   type Entity = World '<a>FieldOf</a>
--   </pre>
--   
--   which is the only form of the <tt>World</tt> that most users of
--   ecstasy will need to interact with.
--   
--   Throughout this document there are references to the <tt>HasWorld</tt>
--   and <tt>HasWorld'</tt> classes, which are implementation details and
--   provided automatically by the library.
module Data.Ecstasy

-- | Data kind used to parameterize the fields of the ECS record.
data ComponentType

-- | This component can be owned by any entity.
Field :: ComponentType

-- | This component can be owned by only a single entity at a time.
Unique :: ComponentType

-- | This component is owned by another system.
Virtual :: ComponentType

-- | A type family to be used in your ECS recrod.

-- | The default world, which contains only empty containers.
defStorage :: HasWorld world m => world ( 'WorldOf m)

-- | Data kind used to parameterize the ECS record.
data StorageType

-- | Used to describe the actual entity.
FieldOf :: StorageType

-- | Used to construct the world's storage.
WorldOf :: (Type -> Type) -> StorageType

-- | Used to construct a setter to update an entity.
SetterOf :: StorageType

-- | A monad transformer over an ECS given a world <tt>w</tt>.
data SystemT w m a

-- | Evaluate a <a>SystemT</a>.
runSystemT :: Monad m => world ( 'WorldOf m) -> SystemT world m a -> m a

-- | Provides a resumable <a>SystemT</a>. This is a pretty big hack until I
--   come up with a better formalization for everything.
yieldSystemT :: Monad m => SystemState world m -> SystemT world m a -> m (SystemState world m, a)

-- | A monad over an ECS given a world <tt>w</tt>.
type System w = SystemT w Identity

-- | Evaluate a <a>System</a>.
runSystem :: world ( 'WorldOf Identity) -> System world a -> a

-- | The internal state of the <a>SystemT</a> monad.
type SystemState w m = (Int, w ( 'WorldOf m))

-- | Create a new entity.
createEntity :: (HasWorld world m, Monad m) => world  'FieldOf -> SystemT world m Ent

-- | The default entity, owning no components.
newEntity :: HasWorld' world => world  'FieldOf

-- | Fetches an entity from the world given its <a>Ent</a>.
getEntity :: (HasWorld world m, Monad m) => Ent -> SystemT world m (world  'FieldOf)

-- | Updates an <a>Ent</a> in the world given its setter.
setEntity :: HasWorld world m => Ent -> world  'SetterOf -> SystemT world m ()

-- | Delete an entity.
deleteEntity :: (HasWorld world m, Monad m) => Ent -> SystemT world m ()

-- | Map a <a>QueryT</a> transformation over all entites that match it.
emap :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m (world  'SetterOf) -> SystemT world m ()

-- | Collect the results of a monadic computation over every entity
--   matching a <a>QueryT</a>.
efor :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m a -> SystemT world m [a]

-- | Do an <a>emap</a> and an <a>efor</a> at the same time.
eover :: (HasWorld world m, Monad m) => EntTarget world m -> QueryT world m (a, world  'SetterOf) -> SystemT world m [a]

-- | The default setter, which keeps all components with their previous
--   value.
unchanged :: HasWorld' world => world  'SetterOf

-- | A setter which will delete the entity if its <a>QueryT</a> matches.
delEntity :: HasWorld' world => world  'SetterOf

-- | An <a>EntTarget</a> is a set of <a>Ent</a>s to iterate over.
type EntTarget world m = SystemT world m [Ent]

-- | Iterate over all entities.
allEnts :: Monad m => EntTarget world m

-- | Iterate over some entities.
someEnts :: Monad m => [Ent] -> EntTarget world m

-- | Iterate over an entity.
anEnt :: Monad m => Ent -> EntTarget world m

-- | A computation to run over a particular entity.
data QueryT w m a

-- | Run a <a>QueryT</a> over a particular <a>Ent</a>.
runQueryT :: (HasWorld world m, Monad m) => Ent -> QueryT world m a -> SystemT world m (Maybe a)

-- | Get the value of a component, failing the <a>QueryT</a> if it isn't
--   present.
query :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m a

-- | Only evaluate this <a>QueryT</a> for entities which have the given
--   component.
with :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m ()

-- | Only evaluate this <a>QueryT</a> for entities which do not have the
--   given component.
without :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m ()

-- | Get the <a>Ent</a> for whom this query is running.
queryEnt :: Monad m => QueryT world m Ent

-- | Attempt to get the value of a component.
queryMaybe :: Monad m => (world  'FieldOf -> Maybe a) -> QueryT world m (Maybe a)

-- | Query a flag as a <a>Bool</a>.
queryFlag :: Monad m => (world  'FieldOf -> Maybe ()) -> QueryT world m Bool

-- | Perform a query with a default.
queryDef :: Monad m => z -> (world  'FieldOf -> Maybe z) -> QueryT world m z

-- | Describes how we can change an <tt>a</tt>.
data Update a

-- | Keep the current value.
Keep :: Update a

-- | Delete the current value if it exists.
Unset :: Update a

-- | Set the current value.
Set :: !a -> Update a

-- | Turn a <a>Maybe</a> into an <a>Update</a>.
maybeToUpdate :: Maybe a -> Update a

-- | The key for an entity.
data Ent

-- | A collection of methods necessary to dispatch reads and writes to a
--   <a>Virtual</a> component.
data VTable m a
VTable :: !(Ent -> m (Maybe a)) -> !(Ent -> Update a -> m ()) -> VTable m a

-- | Get the value of an entity's component.
[vget] :: VTable m a -> !(Ent -> m (Maybe a))

-- | Update the value of an entity's component.
[vset] :: VTable m a -> !(Ent -> Update a -> m ())

-- | Representable types of kind *. This class is derivable in GHC with the
--   DeriveGeneric flag on.
class Generic a