# Computation Expression

### TaskResultOption Computation Expression

Namespace: `FsToolkit.ErrorHandling`

### Examples

#### Example 1

The [TaskResultOption.map2 example](https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling/map2#example-1) can be written using the `taskResultOption` computation expression as below:

```fsharp
// Task<Result<UserTweet option, exn>>
taskResultOption {
  let! post = getPostById samplePostId
  let! user = getUserById post.UserId
  return userTweet post user
}
```

#### Example 2

The `taskResultOption` CE supports binding from multiple compatible types, allowing you to mix `TaskResultOption`, `TaskResult`, `Result`, `Option`, `Task`, and `Async` values without manual conversion:

```fsharp
// parseMode: string -> Result<Mode, string>
// loadUniverse: Mode -> Task<Result<Universe, string>>

// Task<Result<Report option, string>>
taskResultOption {
  // Bind from Result<Mode, string> directly (no manual conversion needed)
  let! mode = parseMode "fast"

  // Bind from Task<Result<Universe, string>> directly
  let! universe = loadUniverse mode

  return generateReport universe
}
```

#### Supported Source Types

The `taskResultOption` CE supports `let!` and `return!` with the following types:

| Type                               | Behavior                                          |
| ---------------------------------- | ------------------------------------------------- |
| `Task<Result<'ok option, 'error>>` | Identity (the CE's native type)                   |
| `Task<Result<'ok, 'error>>`        | `Ok` value is wrapped in `Some`                   |
| `Task<'ok option>`                 | `Some`/`None` is wrapped in `Ok`                  |
| `Task<'ok>`                        | Value is wrapped in `Some` and then `Ok`          |
| `Result<'ok, 'error>`              | `Ok` value is wrapped in `Some`, lifted to `Task` |
| `Choice<'ok, 'error>`              | Converted to `Result`, then same as `Result`      |
| `'ok option`                       | `Some`/`None` wrapped in `Ok`, lifted to `Task`   |
| `Async<Result<'ok, 'error>>`       | `Ok` value is wrapped in `Some`                   |
| `Async<'ok>`                       | Value is wrapped in `Some` and then `Ok`          |