Repository F# setup
open System
open System.IO
open System.Threading
open System.Threading.Tasks
open Axial
open Axial.Layers
open Axial.Console
open Axial.FileSystem
open Axial.Hosting
open Axial.Hosting.Browser
open Axial.Hosting.Node
open Axial.PlatformService
open Axial.State
open Axial.Telemetry
open Axial.Telemetry.JavaScriptAxial.PlatformService exposes five capabilities as dependencies instead of ambient state:
DateTimeOffset.UtcNow, a logger, Random, Guid.NewGuid(), and Environment.GetEnvironmentVariable. Tests can then pin the time or generated identifier.
open System
open Axial
open Axial.PlatformService
SystemAxialPlatformService| Service | Replaces | Module |
|---|---|---|
IClock |
DateTimeOffset.UtcNow |
Clock |
ILog |
An ambient logger | Log |
IRandom |
System.Random |
Random |
IGuid |
Guid.NewGuid() |
Guid |
IEnvironmentVariables |
Environment.GetEnvironmentVariable |
EnvironmentVariables, EnvironmentVariable |
A function that declares IHasClock can be tested at a chosen instant:
let isExpired (expiry: DateTimeOffset) : Flow<#IHasClock, Never, bool> =
Clock.now |> Flow.map (fun now -> now >= expiry)
isExpired: DateTimeOffset -> Flow<'a,Never,bool>expiry: DateTimeOffsetSystem.DateTimeOffsetRepresents a point in time, typically expressed as a date and time of day, relative to Coordinated Universal Time (UTC).
Axial.Flow`3Axial.IHasClockDeclares the clock required by timed workflows and fiber diagnostics.
Axial.NeverRepresents an error channel that cannot occur.
boolAn abbreviation for the CLI type . Basic Types
Axial.PlatformService.ClockHelpers for the clock service.
now: Flow<'env,'error,DateTimeOffset>Reads the current UTC timestamp from an explicit clock service.
(|>): 'T1 -> ('T1 -> 'U) -> 'UApply a function to a value, the value being on the left, the function on the right The argument. The function. The function result. let doubleIt x = x * 2 3 |> doubleIt // Evaluates to 6
Axial.Flowmap: ('value -> 'next) -> Flow<'env,'error,'value> -> Flow<'env,'error,'next>Transforms the successful value of a flow. If the source fails, the is not executed. The original failure cause is preserved, including typed failures, interruption, and defects. Use map for pure value transformations after an effect has succeeded. A function of type 'value -> 'next to transform the successful value. The source flow of type to transform. A new with the transformed success value of type 'next. let flow = Flow.succeed 1 |> Flow.map (fun x -> x + 1)
now: DateTimeOffset(>=): 'T -> 'T -> boolStructural greater-than-or-equal The first parameter. The second parameter. The result of the comparison. 5 >= 1 // Evaluates to true 5 >= 5 // Evaluates to true [1; 5] >= [1; 6] // Evaluates to false
The base runtime
Applications usually need all five. BaseRuntime bundles them, and it
implements one contract per service, so a workflow requiring any combination is satisfied by the single value:
let liveRuntime : BaseRuntime = BaseRuntime.liveValue
liveRuntime: BaseRuntimeAxial.PlatformService.BaseRuntimeGroups the standard operational services commonly used by workflow hosts.
Axial.PlatformService.BaseRuntimeModuleHelpers for constructing the standard explicit service bundle used by workflow hosts.
liveValue: BaseRuntimeCreates the standard live base runtime as an explicit service bundle.
BaseRuntime.live : Layer<unit, Never, BaseRuntime> provides the same bundle to a layer-composed runtime, and
BaseRuntime.fromServiceProvider : Layer<IServiceProvider, BaseRuntimeError, BaseRuntime> builds it from a host
container, turning missing registrations into typed startup errors.
Most applications extend BaseRuntime rather than replacing it; see
Tutorial: Composing Built-in Services for the composition, and
platform services getting started for the shortest path to a
running host.
Deterministic implementations
Every module ships test doubles beside its live value, so a test rarely needs to write an object expression:
let fixedRuntime : BaseRuntime =
{ Clock = Clock.fromValue (DateTimeOffset.Parse "2026-01-01T00:00:00Z")
Log = Log.live
Random = Random.fromValue 7
Guid = Guid.fromValue (System.Guid.Parse "00000000-0000-0000-0000-000000000001")
EnvironmentVariables = EnvironmentVariables.fromPairs [ "AXIAL_ENV", "test" ] }
fixedRuntime: BaseRuntimeAxial.PlatformService.BaseRuntimeGroups the standard operational services commonly used by workflow hosts.
Clock: IClockAxial.PlatformService.ClockHelpers for the clock service.
fromValue: DateTimeOffset -> IClockCreates a deterministic clock that always returns the supplied instant; measured durations are zero.
System.DateTimeOffsetRepresents a point in time, typically expressed as a date and time of day, relative to Coordinated Universal Time (UTC).
Parse: string -> DateTimeOffsetConverts the specified string representation of a date, time, and offset to its equivalent. A string that contains a date and time to convert. An object that is equivalent to the date and time that is contained in . The offset is greater than 14 hours or less than -14 hours. is . does not contain a valid string representation of a date and time. -or- contains the string representation of an offset value without a date or time.
Log: ILogAxial.PlatformService.LogHelpers for the logging service.
live: ILogCreates a no-op logger for tests and local service bundles.
Random: IRandomAxial.PlatformService.RandomHelpers for the random-number service.
fromValue: int -> IRandomCreates a deterministic random generator that always returns the supplied value. NextDouble returns the value as a float and NextBytes truncates it to a byte; use Random.fromFixed when a test needs distinct integer, double, and byte values.
Guid: IGuidAxial.PlatformService.GuidHelpers for the GUID service.
fromValue: Guid -> IGuidCreates a deterministic GUID service that always returns the supplied value.
SystemParse: string -> GuidConverts the string representation of a GUID to the equivalent structure. The string to convert. A structure that contains the value that was parsed. is . is not in a recognized format.
System.GuidRepresents a globally unique identifier (GUID).
EnvironmentVariables: IEnvironmentVariablesAxial.PlatformService.EnvironmentVariablesHelpers for the environment-variable service.
fromPairs: (string * string) seq -> IEnvironmentVariablesCreates a deterministic provider from a fixed set of name/value pairs.
Clock.fromValue, Guid.fromValue, Random.fromValue, Random.fromFixed, EnvironmentVariables.fromPairs, and
Log.fromSink each pin one service to a known answer.
In this section
- Clock: the current instant, and why it belongs in the environment.
- Logging:
ILoglevels, sinks, and its relationship to telemetry. - Randomness and GUIDs: non-determinism you can pin in a test.
- Environment variables: typed reads with
EnvironmentVariableError.