FsToolkit.ErrorHandling 5.0.0

FsToolkit.ErrorHandling

FsToolkit.ErrorHandling is a utility library to work with the Result type in F#, and allows you to do clear, simple and powerful error handling.

The library provides utility functions like map, bind, apply, traverse, sequence as well as computation expressions and infix operators to work with Result<'a, 'b>, Result<'a option, 'b>, Async<Result<'a, 'b>>, Async<Result<'a option, 'b>>, and Result<'a, 'b list>.

It was inspired by Chessie and Cvdm.ErrorHandling (the latter has now been merged into FsToolkit.ErrorHandling).

FsToolkit.ErrorHandling targets .NET Standard 2.0, .NET Standard2.1 and supports Fable.

Documentation

The documentation is available here.

Further material

The main resource as to learning this style of programming Railway Oriented Programming
However Result isn't a panacea, see what pitfalls and where you shouldn't use Result. In defense of Exceptions: Throw (away) your Result

Builds

GitHub Actions

NuGet

Package name	Release	Prelease
FsToolkit.ErrorHandling
FsToolkit.ErrorHandling.TaskResult
FsToolkit.ErrorHandling.JobResult
FsToolkit.ErrorHandling.AsyncSeq
FsToolkit.ErrorHandling.IcedTasks

Developing locally

Devcontainer

This repository has a devcontainer setup for VSCode. For more information see:

VSCode

Local Setup

.NET Core SDK
- v6.x
- v7.x
- v8.x

Optional

To test fable builds locally you will need:

Node
- v18.0.0 or Higher
- Not required but recommend that you use NVM to easily manage multiple versions of Node
Python
- v3.10.0 or higher
- Required for Fable-Python

Compiling

> build.cmd <optional buildtarget> // on windows
$ ./build.sh  <optional buildtarget>// on unix

Without specifying a build target, the default target is DotnetPack, which will run tests for all projects on dotnet and then pack the projects into nuget packages. For additional notable targets see below.

Build Targets

Clean - Will clean all projects bin and obj folders
DotnetTest - Will run tests for dotnet projects
NpmTest - Will run tests for fable-javascript projects
PythonTest - Will run tests for fable-python projects
RunTests - Will run tests for dotnet, fable-javascript and fable-python projects
FormatCode - Will run fantomas to format the codebase

This is not an exhaustive list. Additional targets can be found in the ./build/build.fs file.

A motivating example

This example of composing a login flow shows one example of how this library can aid in clear, simple, and powerful error handling, using just a computation expression and a few helper functions. (The library has many more helper functions and computation expressions as well as infix operators; see the documentation for details.)

// Given the following functions:
//   tryGetUser: string -> Async<User option>
//   isPwdValid: string -> User -> bool
//   authorize: User -> Async<Result<unit, AuthError>>
//   createAuthToken: User -> Result<AuthToken, TokenError>

type LoginError = InvalidUser | InvalidPwd | Unauthorized of AuthError | TokenErr of TokenError

let login (username: string) (password: string) : Async<Result<AuthToken, LoginError>> =
  asyncResult {
    // requireSome unwraps a Some value or gives the specified error if None
    let! user = username |> tryGetUser |> AsyncResult.requireSome InvalidUser

    // requireTrue gives the specified error if false
    do! user |> isPwdValid password |> Result.requireTrue InvalidPwd

    // Error value is wrapped/transformed (Unauthorized has signature AuthError -> LoginError)
    do! user |> authorize |> AsyncResult.mapError Unauthorized

    // Same as above, but synchronous, so we use the built-in mapError
    return! user |> createAuthToken |> Result.mapError TokenErr
  }

Sponsor(s)

Showing the top 20 packages that depend on FsToolkit.ErrorHandling.

Packages	Downloads
FsToolkit.ErrorHandling.TaskResult FsToolkit.ErrorHandling is an extensive utility library based around the F# Result type, enabling consistent and powerful error handling.	16
NBomber Very simple load testing framework for Pull and Push scenarios.	15
FsToolkit.ErrorHandling.TaskResult FsToolkit.ErrorHandling is a utility library to work with the Result type in F#, and allows you to do clear, simple and powerful error handling.	15
FsToolkit.ErrorHandling.TaskResult FsToolkit.ErrorHandling is an extensive utility library based around the F# Result type, enabling consistent and powerful error handling.	15
NBomber Very simple load testing framework for Pull and Push scenarios.	14
FsToolkit.ErrorHandling.TaskResult FsToolkit.ErrorHandling is an extensive utility library based around the F# Result type, enabling consistent and powerful error handling.	14
FsToolkit.ErrorHandling.TaskResult FsToolkit.ErrorHandling is a utility library to work with the Result type in F#, and allows you to do clear, simple and powerful error handling.	14
FsToolkit.ErrorHandling.TaskResult Package Description	14

- BREAKING: [Remove Ply and update to FSharp 6](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/248) Credits @TheAngryByrd - BREAKING: [Remove MergeSources (and!) from some implementations like Result](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/261) Credits @TheAngryByrd - BREAKING: [Merge TaskResult into Core library](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/285) Credits @TheAngryByrd - This means FsToolkit.ErrorHandling.TaskResult is no longer a separate package and will not be updated. It is now part of the core library. - BREAKING: [Rename retn to singleton](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/287) Credits @1eyewonder - BREAKING: [Rename returnError to error + documentation](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/311) Credits @tw0po1nt - [Use Microsoft.Bcl.AsyncInterfaces in netstandard2.0 (Allows IAsyncDisposable and IAsyncEnumerable)](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/250) Credits @TheAngryByrd - [Build against Net8](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/251) Credits @TheAngryByrd - [Fix Overload Resolution to Align to Computation Expression used](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/252) Credits @TheAngryByrd - [refactor!: Seq.sequenceResultM returns Array instead of seq](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/255) Credits @bartelink - [feat(Seq): sequenceResultA](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/255) Credits @bartelink - [Updated uses of Seq.append](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/290) Credits @1eyewonder - [Add Option.traverseAsync and Option.sequenceAsync](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/298#event-15827853276) Credits @tw0po1nt - [Add Require and Check helper methods](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/295) Credits @PI-Gorbo - [Add new AsyncOption APIs and document all its other functions; minor fixes to documentation for Option module](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/307) Credits @tw0po1nt - [F# 9 support and nullness](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/308) Credits @TheAngryByrd - [Update IcedTasks 0.11.7](https://github.com/demystifyfp/FsToolkit.ErrorHandling/commit/0a4cc7b3c52efcef47dbc653b00d56ab029bbd01) Credits @TheAngryByrd - [Add TaskValidation module](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/313) Credits @tw0po1nt - [feat(Seq.traverse/sequence*)!: Yield arrays](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/310) Credits @bartelink - [Add ParallelAsync CEs](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/318) Credits @njlr - [Add Option.sequenceAsyncResult and Option.traverseAsyncResult](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/321) Credits @JayWearsSocks - [Add traversals/sequences for Task and TaskResult in the Option module](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/325) Credits @tw0po1nt - [Add ok and error helper functions to TaskResultOption and AsyncResultOption modules](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/327) Credits @tw0po1nt - [Add CancellableTaskOption module and CE + tests and documentation](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/328) Credits @tw0po1nt - [Remove paket, Enforce nullness on net9.0, remove mocha](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/331) Credits @TheAngryByrd - [Add TaskValueOption module, operators, and CE + tests and documentation](https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/329) Credits @tw0po1nt

.NET 9.0

FSharp.Core (>= 9.0.300)

.NET Standard 2.0

FSharp.Core (>= 6.0.4)
Microsoft.Bcl.AsyncInterfaces (>= 6.0.0)

.NET Standard 2.1

FSharp.Core (>= 6.0.4)

Version	Downloads	Last updated
5.0.0	5	06/06/2025
5.0.0-beta014	5	06/06/2025
5.0.0-beta013	4	06/06/2025
5.0.0-beta012	8	05/04/2025
5.0.0-beta011	8	04/01/2025
5.0.0-beta010	10	03/29/2025
5.0.0-beta009	10	03/05/2025
5.0.0-beta008	7	03/03/2025
5.0.0-beta007	10	02/27/2025
5.0.0-beta006	8	02/27/2025
5.0.0-beta005	10	02/19/2025
5.0.0-beta004	11	02/14/2025
5.0.0-beta003	13	01/12/2025
5.0.0-beta002	12	01/01/2025
5.0.0-beta001	10	12/11/2024
4.18.0	13	11/28/2024
4.18.0-beta001	13	11/28/2024
4.17.0	10	10/06/2024
4.17.0-beta002	10	11/28/2024
4.17.0-beta001	12	10/06/2024
4.16.0	9	11/28/2024
4.15.3	13	10/06/2024
4.15.3-beta001	9	10/06/2024
4.15.2	13	10/06/2024
4.15.2-beta001	8	10/06/2024
4.15.1	12	11/28/2024
4.15.0	12	11/28/2024
4.14.0	13	10/06/2024
4.13.0	10	10/06/2024
4.13.0-beta002	9	10/22/2024
4.13.0-beta001	10	10/23/2024
4.12.0	13	10/06/2024
4.11.1	13	10/06/2024
4.11.0	13	10/06/2024
4.10.0	10	10/06/2024
4.9.0	8	11/28/2024
4.8.0	12	11/06/2024
4.7.0	8	11/28/2024
4.7.0-beta001	12	10/06/2024
4.6.0	12	10/06/2024
4.6.0-beta001	13	11/08/2024
4.5.0	9	11/14/2024
4.5.0-beta002	13	11/09/2024
4.5.0-beta001	10	10/06/2024
4.4.0	12	11/11/2024
4.3.0	12	10/06/2024
4.2.1	11	10/22/2024
4.2.0	9	10/20/2024
4.1.0	12	10/06/2024
4.1.0-beta001	13	10/23/2024
4.0.0	11	11/28/2024
4.0.0-beta001	13	10/22/2024
3.3.1	12	10/22/2024
3.3.1-beta004	10	10/06/2024
3.3.1-beta003	12	10/26/2024
3.3.1-beta002	10	11/21/2024
3.3.1-beta001	10	11/28/2024
3.3.0-beta001	9	11/28/2024
3.2.0	11	11/28/2024
3.2.0-beta001	14	11/06/2024
3.1.0	11	11/12/2024
3.0.1	10	10/06/2024
3.0.0	8	11/28/2024
3.0.0-beta008	12	10/20/2024
3.0.0-beta007	10	10/06/2024
3.0.0-beta006	12	10/06/2024
3.0.0-beta005	13	10/22/2024
3.0.0-beta004	12	10/06/2024
3.0.0-beta003	12	10/22/2024
3.0.0-beta002	10	11/28/2024
3.0.0-beta001	13	11/28/2024
2.13.0	8	11/28/2024
2.13.0-beta001	10	10/06/2024
2.12.0	11	11/28/2024
2.12.0-beta001	10	10/23/2024
2.11.1	12	10/06/2024
2.11.1-beta001	12	10/06/2024
2.11.0	9	11/28/2024
2.11.0-beta004	13	10/23/2024
2.11.0-beta002	13	10/06/2024
2.11.0-beta001	11	11/28/2024
2.10.0	11	11/28/2024
2.9.0	9	10/06/2024
2.9.0-beta001	9	11/28/2024
2.8.1	10	10/06/2024
2.8.0	9	10/06/2024
2.8.0-beta001	13	11/28/2024
2.7.1	7	11/28/2024
2.7.1-beta001	10	11/28/2024
2.7.0	9	11/28/2024
2.7.0-beta001	13	11/28/2024
2.6.0	12	11/28/2024
2.6.0-beta001	12	11/05/2024
2.5.0	9	10/06/2024
2.5.0-beta001	13	10/06/2024
2.4.0	9	10/06/2024
2.4.0-beta001	13	10/20/2024
2.3.0	9	10/21/2024
2.3.0-beta002	12	10/06/2024
2.2.0	13	10/06/2024
2.1.2	9	10/06/2024
2.1.1	12	10/06/2024
2.1.1-beta001	10	10/06/2024
2.1.0	13	10/06/2024
2.1.0-beta003	13	11/28/2024
2.1.0-beta002	13	10/06/2024
2.1.0-beta001	13	10/06/2024
2.0.0	13	11/28/2024
2.0.0-beta002	9	10/23/2024
2.0.0-beta001	13	10/06/2024
1.4.3	12	10/22/2024
1.4.0	9	10/06/2024
1.3.2	11	10/24/2024
1.3.1	12	10/06/2024
1.3.1-beta001	10	11/28/2024
1.3.0	12	10/06/2024
1.3.0-beta006	11	10/22/2024
1.3.0-beta005	13	10/26/2024
1.3.0-beta004	12	11/28/2024
1.2.6	11	11/28/2024
1.2.5	12	10/06/2024
1.2.4	12	11/28/2024
1.2.3	8	11/28/2024
1.2.2	12	11/28/2024
1.2.1	13	10/06/2024
1.1.1	11	10/22/2024
1.1.0	9	10/27/2024
1.0.0	12	10/06/2024
0.0.14	9	11/28/2024
0.0.13	12	11/28/2024
0.0.12	8	10/26/2024
0.0.11	12	11/28/2024
0.0.10	9	11/28/2024
0.0.9	8	11/28/2024
0.0.8	11	11/28/2024
0.0.7	8	10/22/2024
0.0.6	11	11/28/2024
0.0.5	9	10/27/2024
0.0.4	12	10/06/2024
0.0.3	11	10/23/2024
0.0.2	10	10/06/2024
0.0.1	11	11/28/2024