Chain

chain is a small Go workflow library built around composable Action values. An action receives one value, returns the next value, and can be connected to other actions through a Workflow.

The package focuses on in-process workflow control. It does not try to be a distributed scheduler or a full parallel DAG engine.

Installation

go get github.com/JSYoo5B/chain

Core Concepts

Action

An Action is the basic execution unit.

type Action[T any] interface {
    Name() string
    Run(ctx context.Context, input T) (output T, err error)
}

Use NewSimpleAction when a function is enough:

double := chain.NewSimpleAction(
    "double",
    func(ctx context.Context, input int) (int, error) {
        return input * 2, nil
    },
)

Workflow

A Workflow connects actions and also implements Action, so workflows can be nested inside other workflows.

workflow := chain.NewWorkflow("calculation", action1, action2, action3)

output, err := workflow.Run(context.Background(), input)

By default, actions are connected through the Success direction in constructor order. Failure and Abort terminate unless a custom RunPlan is set.

workflow.SetRunPlan(action1, chain.DefaultPlan(action2, errorHandler))

Directions and Run Plans

A RunPlan maps a direction to the next action.

type RunPlan[T any] map[string]Action[T]

Built-in directions are:

• Success
• Failure
• Abort

BranchAction can add custom directions.

Action Builders

Basic Actions

• NewSimpleAction creates an action from a function.
• NewSimpleBranchAction creates a branch action from functions.
• AsBranchAction wraps an existing action and adds branching logic.

Error Control

• AsRetryableAction retries a main action and optionally runs rollback before the next attempt.
• SkipRollback explicitly disables rollback for a retryable action.
• AsBestEffortAction suppresses a non-critical action error and optionally calls a fallback hook.

Collection Processing

• AsSequenceSliceAction runs an action over a slice sequentially.
• AsSequenceMapAction runs an action over a map sequentially.
• AsParallelSliceAction runs an action over a slice concurrently.
• AsParallelMapAction runs an action over a map concurrently.

Parallel collection actions preserve output positions or keys, but joined error order follows completion order.

Type Adaptation

• AdaptAction runs an action against a field or sub-value inside a larger value.

This is useful when a workflow carries one aggregate state type, while some actions only operate on one part of that state.

Validation

Workflow.ValidateGraph checks the configured workflow graph before execution.

It rejects:

• directed cycles
• disconnected workflow graphs

Branching and merge points are allowed as long as the graph remains a connected DAG.

Examples

See:

• examples/branch
• examples/adapter
• docs/action-patterns.md