# Computation Expression

### JobResult Computation Expression

Namespace: `FsToolkit.ErrorHandling`

### Examples

#### Example 1

The initial [motivating example](https://github.com/demystifyfp/FsToolkit.ErrorHandling/blob/master/README.md) is perhaps more realistic if some functions are asynchronous. Given the following functions:

```fsharp
tryGetUser : string -> Job<User option>
isPwdValid : string -> User -> bool
authorize : User -> Job<Result<unit, AuthError>>
createAuthToken : User -> Result<AuthToken, TokenError>
```

A login flow can be implemented as below using the `jobResult` CE and a few [helpers](https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling.jobresult/jobresult/broken-reference):

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

let login (username: string) (password: string) : Job<Result<AuthToken, LoginError>> =
  jobResult {
    let! user = username |> tryGetUser |> JobResult.requireSome InvalidUser
    do! user |> isPwdValid password |> Result.requireTrue InvalidPwd
    do! user |> authorize |> JobResult.mapError Unauthorized
    return! user |> createAuthToken |> Result.mapError TokenErr
  }
```