Execution and Outcomes

Flow<'env, 'error, 'value> is cold. Building a workflow does not run it.

Execution starts only at an explicit boundary:

let workflow = Flow.succeed "Hello"

let exit = workflow.RunSynchronously(())

On .NET you can choose the platform handle:

let valueTask = workflow.ToValueTask(env)
let task = workflow.ToTask(env)
let asyncWork = workflow.ToAsync(env)

On Fable, use:

let asyncWork = workflow.ToAsync(env)

ToValueTask, ToTask, and ToAsync start the workflow and return a platform handle. They do not synchronously wait for completion. Await or run the returned handle to observe the final Exit<'value, 'error>.

Exit

Execution completes with Exit<'value, 'error>, which is FsFlow’s name for Result<'value, Cause<'error>>. It has a distinct name because it describes the completed state of a workflow execution, not just an ordinary domain success or failure.

match exit with
| Exit.Success value ->
    printfn "Succeeded: %A" value
| Exit.Failure cause ->
    printfn "Failed: %s" (Cause.prettyPrint string cause)

Cause<'error> distinguishes typed failures from defects and interruption:

Converting to Result

Use Exit.toResult only at boundaries that need standard F# Result:

task {
    let! exit = workflow.ToTask(env)
    return Exit.toResult exit
}

Exit.toResult raises for defects, interruption, and composite causes because Result cannot represent those outcomes without losing information.