Ideas for more flexibility, performance, and usability

[spacekitteh]

1. Split ComponentType into two new types, MembershipType (for Field and Virtual) and Semantics (Unique). This might allow easier extensions in both directions, such as adding Flag semantics and Required membership.

2. Allow user-defined storage equations, particularly for WorldOf. For example, if the previous idea isn't implemented, this would still allow many of the same performance benefits, such as using compressed bitmaps for Boolean values, or unboxed Vectors for positions/velocities/etc.

3. Expose an optical interface!

[spacekitteh]

Some more concrete syntax ideas:

Style #1:

do
    pos@(Position x y)<- with
    vel <- with @Velocity
    Not @Flying <- with
    pos.x += vel.x

Style #2:

process l a = do
    ecs <- get
    iforMOf l ecs a

movement =
    process (with @Position . with @Velocity . with @(Not Flying)) $ \ent (position, velocity) -> do
        position.x += velocity.x
        if ent `in` bosses then
            putStrLn "gotta go fast"
            else pure ()

Style #2 seems like it would be more amenable to having GHC.Generics produce the correct code to minimise traversal, pushing the filtering of entities into the traversal code, and not relying on, say, Alternative/MonadPlus instances.