System effect

[Trouv]

I started implementing a SystemEffect that wraps around systems that return effects. It's kinda a theoretically satisfying construction, making the affect system double as a "system application" system.

This issue is for finishing such an effect.

I think it could also be used for slightly more complex versions of the existing effects that accept functions that return effects, like CommandSpawnAnd and AssetServerLoadAnd. So, it should be generic over SystemInput to support these cases. Though, maybe it only implements Effect in the SystemInput=() case. OR maybe these systemic versions of these effects just use plain impl SystemParamFunctions and avoid the issue entirely.