Sketch: Atomics and Mutation

What does it look like to mutate state outside of the scope of a function?

Problem Statement

I want the ability to modify, in-place, the value of some reference or some value on the stack. I want the ability to do this outside of the scope of a single function.

Example Functionality

What is a State? How is a state_set implementation possible?

fn example: State String -> String -> IO Unit
    λ state newValue => state_set state newValue
end fn

Problem: Thread-Safe Access

All access to the State "thing" must be thread-safe.

Problem: Representation

Ava, to this point, has not had any record-mutable state or the notion of such an object.
Ava does not and will not have inheritance (precondition).
Must Ava have a mutable primitive?
How could Ava support mutability without direct access? This implies that something like mut as a record field modifier is not sufficient.

Idea: Support via Modifiers

The following implementation is incomplete and does not enforce any thread safety, but illustrates how private access could help this work.

Also, it demonstrates that anonymous function syntax needs to be considered.

given A
record State
    private mut data: A,
end record

given A
fn state_get: State A -> IO A
    λ state => defer (λ => state.data)
end fn

given A
fn state_set: State A -> A -> IO State A
    λ state newValue => map (defer (λ => state.data = newValue)) (λ => state)
end fn

given A
fn state_modify: State A -> (A -> A) -> IO State A
    λ state f =>
        map
            (defer λ => state.data = f state.data)
            λ => state

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