# apecs

Fast Entity-Component-System library for game programming https://github.com/jonascarpay/apecs#readme

 LTS Haskell 16.16: 0.9.2 Stackage Nightly 2020-09-29: 0.9.2 Latest on Hackage: 0.9.2

See all snapshots apecs appears in

Maintained by

#### Module documentation for 0.9.2

This version can be pinned in stack with:apecs-0.9.2@sha256:0cedc4c7c6c33e387f5fe1ea7b606779642439e1c498053c34c51aaa88abbe3d,2098

# apecs

apecs is an Entity Component System (ECS) library for game development.

apecs aims to be

• Fast - Performance is competitive with Rust ECS libraries (see benchmark results below)
• Safe - Completely hides the dangers of the low-level machinery
• Concise - Game logic is expressed using a small number of powerful combinators
• Flexible - Easily add new modules or backends
• Cool

### Example

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

## [0.9.1]

### Changed

• (#63) Fixed bug where modify on non-existent components crashes

## [0.9.0]

• (#59) Expose makeMapComponents, which creates Component instances with Map stores

### Changed

• (#60) Add Component type names in non-existent component errors
• Relaxed the type of modify to allow a different return type
• Constrain the cmapM_ type (c -> SystemT w m ()) -> SystemT w m (), to make it clearer that the inner function does not update Components
• Simplify nix infrastructure

## [0.8.2]

### Changed

• (#55) Fixed a bug where components where not properly deleted from the cache following the cache bitmasking update

## [0.8.1]

### Changed

• Changed Caches to use bitmasks instead of the remainder operation. This makes caches up to three times faster.
• Fixed bug in Cache where the same entity appeared in member list of both the cache and the underlying store

## [0.8.0]

There are a number of unsolved problems in apecs’ design space. Most notably, it needs a good way to do streaming and reactivity, or find a way to integrate with existing solutions. I’m hesitant to accept some of the feature requests I’ve gotten because they would be obsoleted when we figure this out, and I don’t want to pollute the API with unstable features.

However, I don’t think we should let perfect get in the way of good. So, apecs 0.8 have new Apecs.Experimental.* modules, that I want to use for features that might or might not get removed or changed. They should provide some conveniences, but the catch is that their API might undergo significant changes between point releases (and therefore within LTS’es). Some of the existing modules were already marked experimental, and those have been moved.

• OrdMap and IxMap reactive maps

### Changed

• Moved ReadOnly to Apecs.Stores since EntityCounter now depends on it
• Moved spatial hashing to Experimental.Util
• Moved Redirect and Stores.Extra to Experimental.Stores
• Moved Reactive to Experimental.Reactive
• rget has been replaced by withReactive
• Improved error messages for unsafe operations

## [0.7.3]

### Changed

• Added Data.Semigroup to Stores.Extra to build with GHC 8.2.2 in hackage matrix

## [0.7.2]

### Changed

• Fixed bug in the Pushdown store
• Apecs module no longer re-exports the entire Data.Proxy module, but instead just Proxy (..).
• Added (approximate?) lower and upper version bounds to dependencies

## [0.7.1]

• \$= and \$~ operators as synonyms for set and get respectively

### Removed

• getAll and count, which were made redundant by cfold.

## [0.7.0]

• The Reactive store and module is a redesign of the Register store, and provides a more general solution for ‘stores that perform additional actions when written to’.
• The Apecs.Stores.Extra submodule, which contains the Pushdown and ReadOnly stores. Pushdown adds pushdown semantics to stores, and ReadOnly hides the ExplSet instances of whatever it wraps.
• The EntityCounter and associated functions have all been specified to IO, since Global EntityCounter only works in IO. Furthermore, EntityCounter now uses a ReadOnly store, to prevent users from accidentally changing its value.
• Redirect component that writes to another entity in cmap.

### Changed

• Default stores have MonadIO m => m instances, rather than IO. This makes it easier to nest SystemT.
• All apecs packages have been consolidated into a single git repo.
• Apecs.Components contains the components (and corresponding stores) from Apecs.Core.

## [0.6.0.0]

### Changed

• Nothing, but since 0.5.1 was API-breaking I’ve decided to bump to 0.6

## [0.5.1.1]

### Changed

• Register needs UndecidableInstances in GHC 8.6.2, I’m looking for a way around this. I’ve removed it for now.

## [0.5.1.0]

• The Register store, which allows reverse lookups for bounded enums. For example, if Bool has storage Register (Map Bool), regLookup True will yield a list of all entities with a True component. Can also be used to emulate a hash table, where fromEnum is the hashing function. This allows us to make simple spatial hashes. I’m open to suggestions for better names than Register.
• cmapIf, cmap with a conditional test

### Changed

• ExplInit now too takes a monad argument.
• Started rewrite of the test suite
• Caches now internally use -2 to denote absence, to avoid possible conflict with -1 as a global entity

### Removed

• The STM instances have been removed, to be moved to their own package

## [0.5.0.0]

### Changed

• System w a is now a synonym for SystemT w IO a. A variable monad argument allows apecs to be run in monads like ST or STM. Most of the library has been rewritten to be as permissive as possible in its monad argument.

• STM stores. These will be moved to a separate package soon.

## [0.4.1.2]

### Changed

• Either can now be deleted, deleting Either a b is the same as deleting (a,b).
• Some were missing their inline pragma’s, now they don’t

## [0.4.1.1]

### Changed

• Export Get, Set, Destroy, Members by default
• Export cfold, cfoldM, cfoldM_ by default
• Fix () instance

## [0.4.1.0]

• cfold, cfoldM, cfoldM_
• Either instances and EitherStore

### Changed

• Changed MaybeStore implementation to no longer use -1 for missing entities.
• Fixed some outdated documentation.
• Change the global void entity to -2, just to be sure it won’t conflict if accidentally used in a cache.