kotlin-cor — Chain of Responsibility for Business Logic

kotlin-cor is a lightweight Kotlin Multiplatform library that brings Chain of Responsibility pattern to business logic orchestration. It allows you to write complex business processes as readable, declarative code — instead of XML schemas or visual BPM designers.

Niche & Purpose

kotlin-cor fills the gap between simple CoR pattern and full-blown workflow engines:

Category	Tools	kotlin-cor Role
State Machines	Tinder/StateMachine, KStateMachine	Different — sequential processing, not state transitions
Workflow Engines	Temporal, Infinitic, Conductor	Lighter alternative — no infrastructure needed
Saga Pattern	Arrow Saga	Different — sequential pipeline, not distributed transactions
BPMS	Camunda, Flowable	Direct competitor — code-first instead of visual-first

Primary Use Cases:

• Request handling pipelines (validation → authorization → processing → response)
• Business logic in microservices without external orchestration
• Projects requiring Kotlin Multiplatform (JVM + JS + Native)
• Teams wanting version control over business logic

Competitive Advantages

1. Code-first — Business logic in Kotlin, not XML/BPMN
2. No infrastructure — Just a library, no external servers
3. KMP — Single codebase for all platforms (JVM, JS, Native, Wasm)
4. Readable — Chain reads like documentation
5. Extensible — Easy to add custom handlers

See docs/comparison.md for detailed analysis.

Quick Example

val chain = rootChain<BizContext> {
    validate("Validate request") {
        validateNotEmpty("Check ID not empty")
        validateFormat("Check ID format")
    }
    authorize("Check access rights") {
        fetchUserPermissions()
        checkObjectAccess()
    }
    fetchData("Load business object")
    respond("Prepare response")
}.build()

runBlocking { chain.exec(BizContext(request)) }

Key Features

• Human-readable — business logic reads like a specification
• Kotlin Multiplatform — JVM, JS, Native, Wasm
• Condition-based execution — on { condition } for conditional steps
• Error handling — except blocks for compensation/rollback
• Parallel execution — parallel block for concurrent operations
• Settings support — external configuration injection

Installation

// build.gradle.kts
dependencies {
    implementation("com.crowdproj:kotlin-cor:${VERSION}")
}

Documentation

• Overview
• Core Concepts — Worker, Chain, Parallel, Loop
• DSL Reference
• Examples
• Contributing

Status

• Version: ${VERSION}
• Kotlin: 2.3.20
• Platforms: JVM, JS, Linux, iOS, macOS, tvOS, watchOS, Wasm, Windows, Android Native