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

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

Examples

Example 1

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

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."