[machiaweliczny]

Not a Haskell expert, but I think I know what you mean -you are passing items by value to many functions and complain it's not modified in others, when you call them, or you need to compose flow so updates are properly "bubbled".

But with assumption that code was working before and you had for example function: use :: Item -> Item, and you change duration in this function, what else do you need to change to "bubble" new state? I don't get this.

BTW What's the problem with global store and passing only IDs ? I feel like this is probably valid approach and anyway ECS are implemented in similar manner AFAIK - https://en.m.wikipedia.org/wiki/Entity_component_system

[tsimionescu]

As I understand it, a function use :: Item -> Item in Haskell guarantees that it can't change any property of any item;even more so if the function were use :: Item -> Effect, as could be done on the initial assumption that Items can't change.

[thedataangel]

In general you can't mutate records. Nothing prevents you from making a new one that's slightly different though. It just won't change the already existing one.

In practice this is not actually a problem. It just takes a little getting used to to get yourself out of the 'memory-address as identity' mindset that procedural languages have.