how to use lambda in vb.net

When I use AngleSharp in VB.NET, the lambda in C# becomes a question. VB.NET can use function to replace lambda but seem to accept only one argument

Dim document = Await context.OpenAsync(Function(Res)
Res.Content("

")
.Address("http://localhost/")
.Header(HeaderNames.SetCookie, my_headers)
End Function
)

The errors:

Error BC30518 Overload resolution failed because no accessible 'OpenAsync' can be called with these arguments:
Extension method 'Public Function OpenAsync(response As IResponse, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'IResponse' because 'IResponse' is not a delegate type.
Extension method 'Public Function OpenAsync(request As DocumentRequest, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'DocumentRequest' because 'DocumentRequest' is not a delegate type.
Extension method 'Public Function OpenAsync(url As Url, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'Url' because 'Url' is not a delegate type.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Leading '.' or '!' can only appear inside a 'With' statement.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Leading '.' or '!' can only appear inside a 'With' statement.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': 'HeaderNames' is not declared. It may be inaccessible due to its protection level.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Leading '.' or '!' can only appear inside a 'With' statement.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Leading '.' or '!' can only appear inside a 'With' statement.
Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': 'HeaderNames' is not declared. It may be inaccessible due to its protection level.
Extension method 'Public Function OpenAsync(address As String, [cancellation As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'String' because 'String' is not a delegate type.

How do I fix it?

the errors after modifying by 41686d6564

Error   BC30518 Overload resolution failed because no accessible 'OpenAsync' can be called with these arguments:
    Extension method 'Public Function OpenAsync(response As IResponse, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'IResponse' because 'IResponse' is not a delegate type.
    Extension method 'Public Function OpenAsync(request As DocumentRequest, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'DocumentRequest' because 'DocumentRequest' is not a delegate type.
    Extension method 'Public Function OpenAsync(url As Url, [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'Url' because 'Url' is not a delegate type.
    Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': 'Return' statement in a Sub or a Set cannot return a value.
    Extension method 'Public Function OpenAsync(request As Action(Of VirtualResponse), [cancel As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': 'HeaderNames' is not declared. It may be inaccessible due to its protection level.
    Extension method 'Public Function OpenAsync(address As String, [cancellation As CancellationToken = Nothing]) As Task(Of IDocument)' defined in 'BrowsingContextExtensions': Lambda expression cannot be converted to 'String' because 'String' is not a delegate type.

Solution

There are two problems with your code:

The overload that you're trying to use takes an Action, not a Func. Therefore, you ought to use Sub instead of Function.
In VB, the dot has to come at the end of the line, not at the beginning of the next one (in C#, you may do either), or else the line continuation character (i.e., _) must be used.

Changing your code to something like the following should make it compile:

Dim document = Await context.OpenAsync(
    Sub(Res)
        Res.Content("").
        Address("http://localhost/").
        Header(HeaderNames.SetCookie, my_headers)
    End Sub)

Or using explicit line continuation:

Dim document = Await context.OpenAsync(
    Sub(Res)
        Res.Content("") _
        .Address("http://localhost/") _
        .Header(HeaderNames.SetCookie, my_headers)
    End Sub)