('a -> 'b) -> ('c -> 'b) -> Async<Result<'a, 'c>> -> Async<'b>
type HttpResponse<'a, 'b> =
| Ok of 'a
| InternalError of 'b
// CreatePostRequest -> Async<Result<PostId, exn>>
let createPost (req : CreatePostRequest) = async {
// ...
}
// Async<HttpResponse>
let handler (httpReq : HttpRequest) =
// ...
// Async<Result<PostId, exn>>
let createPostAR = createPost httpReq
createPostAR
|> AsyncResult.fold Ok InternalError