Write asynchronous F# workflows whose expected failures and required dependencies are visible in their types.

A handler usually needs services and can fail, but a Task signature shows neither fact. Flow<'env, 'error, 'value> makes both part of the contract.

open Axial

type CheckoutError =
    | OrderNotFound of orderId: int
    | PaymentDeclined of reason: string

type Receipt = { OrderId: int; Total: decimal; Reference: string }

type CheckoutEnv =
    { FindTotal: int -> ColdTask<Result<decimal, CheckoutError>>
      Charge: decimal -> ColdTask<Result<string, CheckoutError>> }

let checkout orderId : Flow<CheckoutEnv, CheckoutError, Receipt> =
    flow {
        let! findTotal = Flow.envWith _.FindTotal
        let! charge = Flow.envWith _.Charge
        let! total = findTotal orderId
        let! reference = charge total
        return { OrderId = orderId; Total = total; Reference = reference }
    }

The application supplies live functions. A test supplies a record of fakes. The workflow does not change.

Adding a timeout, a retry policy, and a resource that must be released does not change the signature either, because the runtime that starts the workflow owns cancellation, retries, and cleanup:

open System

let checkoutOrder orderId : Flow<CheckoutEnv, CheckoutError, Receipt> =
    checkout orderId
    |> Flow.Runtime.retry (RetryPolicy.noDelay 3)
    |> Flow.Runtime.timeout (TimeSpan.FromSeconds 5.0) (PaymentDeclined "checkout timed out")

Flow also carries concurrency, scheduling, streams, and structured child fibers through the same runtime.

dotnet add package Axial

• Axial — the core workflow model: typed failures, dependencies, concurrency, resources, schedules, streams, and layers.
• Axial.Process — external process composition, pipelines, streaming output, typed failures, cancellation, and cleanup.
• Axial.HttpClient — typed HTTP requests, response handling, and reliability policies.

Supporting packages provide platform services, console and file-system access, hosting, and telemetry. The package catalogue links the first-class libraries and the complete compatibility matrix.

• Getting started
• Add Axial to an existing Task application
• Failures and defects
• Dependencies and services
• Concurrency
• Process
• HTTP client
• Runnable examples
• Integration reference application

Reified declares value, model, JSON, and HTTP contracts. Axial's optional server adapters execute Reified HTTP contracts as workflows; neither core depends on the other.

Declare a contract with Reified. Serve it with Axial.