Context-aware Flipper

The previous Flipper example stores all values in logic state — a central location that requires sequential access.

With a million users flipping values, each must wait for the previous one to finish.

Actor State: Parallel Execution

MOI solves this by moving data from logic state to actor context. Each actor (user or logic) stores their own value, enabling parallel execution.

A million actors can flip their values simultaneously.

tip

Read more about state in Logic and Actor State.

Modified Code

Create context_flipper.coco:

context_flipper.coco

coco ContextFlipper

state actor:
    value Bool

endpoint dynamic Flip():
    mutate value <- ContextFlipper.Sender.value:
        value = !value

endpoint static Mode() -> (value Bool):
    observe value <- ContextFlipper.Sender.value

endpoint dynamic Set(value Bool):
    mutate value -> ContextFlipper.Sender.value

Key differences:

• state actor instead of state logic
• No initialization endpoint: an actor that has never written value reads it as false, the zero value of Bool
• Access via Sender instead of Logic

Test the Code

coco compile
coco lab init

Flip and Test

Actor state needs no setup step. The sender's value starts as false and changes on the first Flip:

# Never written, so the logic reads the zero value
invoke ContextFlipper.Mode()
# → value:false

invoke ContextFlipper.Flip()
observe ContextFlipper.Sender.value
# → true

note

The observe command reads the stored slot directly, so for a value that has never been written it reports error: value not found. Endpoints never see that error. Inside the logic, an unwritten field reads as its zero value.

Multiple Ways to Observe

All these return the same value:

observe ContextFlipper.Sender.value
observe ContextFlipper.default_user.value
observe ContextFlipper.<identifier>.value

Test with Another User

register Robert
set default.sender Robert

# Each actor has their own value. Robert's has never been written
invoke ContextFlipper.Mode()               # → value:false
observe ContextFlipper.default_user.value  # → true (unchanged)

# Flip Robert's value twice
invoke ContextFlipper.Flip()
observe ContextFlipper.Robert.value        # → true
invoke ContextFlipper.Flip()
observe ContextFlipper.Robert.value        # → false
observe ContextFlipper.default_user.value  # → still true

Actor context is the foundation of parallel execution in MOI.