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https://github.com/demystifyfp/FsToolkit.ErrorHandling
An opinionated F# Library for error handling
https://github.com/demystifyfp/FsToolkit.ErrorHandling
category-theory error-handling fsharp railway-oriented-programming
Last synced: 4 months ago
JSON representation
An opinionated F# Library for error handling
- Host: GitHub
- URL: https://github.com/demystifyfp/FsToolkit.ErrorHandling
- Owner: demystifyfp
- License: mit
- Created: 2018-07-21T20:18:19.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2024-02-14T14:40:11.000Z (5 months ago)
- Last Synced: 2024-02-14T15:48:29.507Z (5 months ago)
- Topics: category-theory, error-handling, fsharp, railway-oriented-programming
- Language: F#
- Homepage: https://demystifyfp.gitbook.io/fstoolkit-errorhandling
- Size: 3.71 MB
- Stars: 430
- Watchers: 11
- Forks: 57
- Open Issues: 14
-
Metadata Files:
- Readme: README.md
- License: License
Lists
- awesome-fsharp - FsToolkit.ErrorHandling - Clear, simple and powerful error handling with railway-oriented programming. Inspired by Chessie. [MIT] (General purpose libraries / Performance analysis)
- awesome-stars - FsToolkit.ErrorHandling
README
# 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>`, `Async>`, and `Result<'a, 'b list>`.
It was inspired by [Chessie](https://github.com/fsprojects/Chessie) and Cvdm.ErrorHandling (the latter has now been merged into FsToolkit.ErrorHandling).
FsToolkit.ErrorHandling targets .NET Standard 2.0 and .NET Framework 4.6.1 and supports Fable.
## Documentation
The documentation is [available here](https://demystifyfp.gitbook.io/fstoolkit-errorhandling).
## Further material
* The main resource as to learning this style of programming [Railway Oriented Programming](https://fsharpforfunandprofit.com/rop/)
* However Result isn't a panacea, see what pitfalls and where you shouldn't use `Result`. [In defense of Exceptions: Throw (away) your Result](https://www.youtube.com/watch?v=E4dI-zd4Cag)
## Builds
GitHub Actions |
:---: |
[](https://github.com/demystifyfp/FsToolkit.ErrorHandling/actions?query=branch%3Amaster) |
[](https://github.com/demystifyfp/FsToolkit.ErrorHandling/actions?query=branch%3Amaster) |
### NuGet
| Package name | Release | Prelease
| --- | --- | --- |
| FsToolkit.ErrorHandling | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling) | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling/absoluteLatest)
| FsToolkit.ErrorHandling.TaskResult | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.TaskResult) | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.TaskResult/absoluteLatest)
| FsToolkit.ErrorHandling.JobResult | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.JobResult) | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.JobResult/absoluteLatest)
| FsToolkit.ErrorHandling.AsyncSeq | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.AsyncSeq) | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.AsyncSeq/absoluteLatest)
| FsToolkit.ErrorHandling.IcedTasks | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.IcedTasks) | [](https://www.nuget.org/packages/FsToolkit.ErrorHandling.IcedTasks/absoluteLatest)
## Developing locally
### Devcontainer
This repository has a devcontainer setup for VSCode. For more infomation see:
- [VSCode](https://code.visualstudio.com/docs/devcontainers/containers)
### Local Setup
* [.NET Core SDK](https://www.microsoft.com/net/download/)
* [v6.x](https://dotnet.microsoft.com/en-us/download/dotnet/6.0)
* [v7.x](https://dotnet.microsoft.com/en-us/download/dotnet/7.0)
#### Optional
To test fable builds locally you will need:
* [Node](https://nodejs.org/en/)
* v18.0.0 or Higher
* Not required but recommend that you use [NVM](https://github.com/nvm-sh/nvm) to easily manage multiple versions of Node
* [Python](https://www.python.org/downloads/)
* v3.10.0 or higher
* Required for Fable-Python
#### Compiling
```bash
> build.cmd // on windows
$ ./build.sh // 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 exhausting 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](https://demystifyfp.gitbook.io/fstoolkit-errorhandling) for details.)
```f#
// Given the following functions:
// tryGetUser: string -> Async
// isPwdValid: string -> User -> bool
// authorize: User -> Async>
// createAuthToken: User -> Result
type LoginError = InvalidUser | InvalidPwd | Unauthorized of AuthError | TokenErr of TokenError
let login (username: string) (password: string) : Async> =
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)
