Module handler 

Effect Handler Architecture for Choreographic Programming

This module provides a clean effect boundary between pure choreographic logic and runtime transport implementations. It allows for testable, composable, and runtime-agnostic protocol implementations.

Architecture

The effect handler system separates concerns:

• Choreographic Logic: Pure protocol specification (what to do)
• Effect Handlers: Runtime implementation (how to do it)
• Interpreters: Execute choreographic programs using handlers
• Contract Profiles: Machine-checkable statements of semantic obligations versus transport-policy freedom, defined in effects::contract

Example

use telltale_runtime::{ChoreoHandler, LabelId};

#[async_trait]
impl ChoreoHandler for MyHandler {
    type Role = MyRole;
    type Endpoint = MyEndpoint;

    async fn send<M>(&mut self, ep: &mut Self::Endpoint, to: Self::Role, msg: &M) -> Result<()> {
        // Implementation
    }
    // ... other methods
}

ProtocolMachine Boundary

The bytecode ProtocolMachine in telltale-machine exposes a separate, synchronous EffectHandler trait for simulation/runtime integration. It is not interchangeable with ChoreoHandler: ChoreoHandler is async and typed over concrete message/role types, while the ProtocolMachine handler operates over bytecode values and must remain session-local for determinism.

Structs

MessageTag

Typed message tag for receive effects.

NoOpHandler

A no-op handler for testing pure choreographic logic

Enums

ChoreographyError

Errors that can occur during choreographic execution

Traits

ChoreoHandler

The core effect handler trait that abstracts all communication effects

ChoreoHandlerExt

Extension trait for handler lifecycle management

ContextExt

Extension trait for adding context to Results.

Endpoint

Session endpoint trait

LabelId

Labels identify branches in internal/external choice.

RoleId

Trait for role identifiers in choreographies

Type Aliases

ChoreoResult

Result type for choreography operations.