apecs
apecs is an Entity Component System (ECS) framework inspired by specs and Entitas.
The front-end DSL uses a small set of combinators to concisely express game logic, which then translate to fast primitive operations on back-end stores.
Both the DSL and storage framework can easily be extended to meet any performance/expressivity needs.
Links
Performance
ecs-bench shows that apecs is competitive with the fastest Rust ECS frameworks.
Example
{-# LANGUAGE DataKinds, ScopedTypeVariables, TypeFamilies, MultiParamTypeClasses, TemplateHaskell #-}
import Apecs
import Linear (V2 (..))
newtype Position = Position (V2 Double) deriving Show
-- To declare a component, we need to specify how to store it
instance Component Position where
type Storage Position = Map Position -- The simplest store is a Map
newtype Velocity = Velocity (V2 Double) deriving Show
instance Component Velocity where
type Storage Velocity = Cache 100 (Map Velocity) -- Caching adds fast reads/writes
data Flying = Flying
instance Component Flying where
type Storage Flying = Map Flying
makeWorld "World" [''Position, ''Velocity, ''Flying] -- Generate World and instances
game :: System World ()
game = do
newEntity (Position 0, Velocity 1)
newEntity (Position 2, Velocity 1)
newEntity (Position 1, Velocity 2, Flying)
-- Add velocity to position
cmap $ \(Position p, Velocity v) -> Position (v+p)
-- Apply gravity to non-flying entities
cmap $ \(Velocity v, _ :: Not Flying) -> Velocity (v - (V2 0 1))
-- Print a list of entities and their positions
cmapM_ $ \(Position p, Entity e) -> liftIO . print $ (e, p)
main :: IO ()
main = initWorld >>= runSystem game