apecs

apecs is an Entity Component System (ECS) library inspired by specs and Entitas. ECS presents a data-driven approach to game development, that elegantly tackles many of the unique issues of game programming.

apecs aims to be

• Fast - Performance is competitive with Rust ECS libraries (see benchmark results below).
• Concise - Game logic is expressed using a small number of powerful combinators.
• Safe - The cmap/cfold-DSL completely hides the dangers of the low-level API.
• Extensible - At its heart apecs is just a data manipulation DSL that can be implemented with any number of backends. As a monad transformer it easily integrates into larger applications.
• Cool

Links

• documentation on hackage
• tutorial and other examples
• paper (prepublication) (see #19)
• apecs-physics - 2D physics using the Chipmunk2D engine
• apecs-gloss - Simple frontend for gloss-based rendering
• apecs-stm - STM-based stores for easy concurrency

By other authors

• An Introduction to Developing Games in Haskell with Apecs by Ashley Smith

Status

Package	Hackage	Stack LTS	Stack Nightly
apecs
apecs-physics
apecs-gloss
apecs-stm		-	-
examples	-	-	-

Example

{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TemplateHaskell       #-}
{-# LANGUAGE TypeFamilies          #-}

import Apecs
import Linear (V2 (..))

newtype Position = Position (V2 Double) deriving Show
newtype Velocity = Velocity (V2 Double) deriving Show
data Flying = Flying

makeWorldAndComponents "World" [''Position, ''Velocity, ''Flying]

game :: System World ()
game = do
  newEntity (Position 0, Velocity 1)
  newEntity (Position 2, Velocity 1)
  newEntity (Position 1, Velocity 2, Flying)

  -- 1. Add velocity to position
  -- 2. Apply gravity to non-flying entities
  -- 3. Print a list of entities and their positions
  cmap $ \(Position p, Velocity v) -> Position (v+p)
  cmap $ \(Velocity v, _ :: Not Flying) -> Velocity (v - V2 0 1)
  cmapM_ $ \(Position p, Entity e) -> liftIO . print $ (e, p)

main :: IO ()
main = initWorld >>= runSystem game