> For the complete documentation index, see [llms.txt](https://demystifyfp.gitbook.io/fstoolkit-errorhandling/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling/result/check.md).

# check

Namespace: `FsToolkit.ErrorHandling`

The intent of check is to allow an Ok result value to be validated.

`check` takes a validation function of the form `'ok -> Result<unit, 'error>` and a result of the form `Result<'ok, 'error>`.

If the result is `Ok x` then the validation function is applied, and if the validation function returns an error, this new error is returned. Otherwise, the original `Ok x` result is returned. If the original result is an Error, the original result is returned.

## Function Signature

```fsharp
('ok -> Result<unit,'error>) -> Result<'ok,'error> -> Result<'ok,'error>
```

## Examples

### Example 1

```fsharp
Ok (
    {|
        AccessPolicyName = "UserCanAccessResource"
        IsEnabled = true
    |}

)
|> Result.check (fun policy ->
    if not policy.IsEnabled then
        Error (
            $"The policy {policy.AccessPolicyName} cannot be used because its disabled."
        )
    else
        Ok ()
)

// Ok {| AccessPolicyName = "UserCanAccessResource"; IsEnabled = true; |}
```

### Example 2

```fsharp
Ok (
    {|
        AccessPolicyName = "UserCanAccessResource"
        IsEnabled = false
    |}

)
|> Result.check (fun policy ->
    if not policy.IsEnabled then
        Error (
            $"The policy {policy.AccessPolicyName} cannot be used because its disabled."
        )
    else
        Ok ()
)

// Error "The policy UserCanAccessResource cannot be used because its disabled."
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling/result/check.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.