Traversal can't change type

[dawnchan030920]

modify and modifyF of traversals both cannot change the type of the value. A more general function is needed.

Scenario

For example, I'm building a blog and I have a slug to some other content collection inside of a list field of a collection item. GetXXXBySlug returns Option<T> and I want the Option to wrap the entire object, and T at the same time not a string.

It requires me to perform a wrapping of a side-effect while also changing the type of the value from string to T.

Example

Change

type Series = {
    posts: {
        postSlug: string;
        subtitle?: string | undefined;
    }[];
    slug: string;
    title: string;
    description: string;
}

into

Option<{
    posts: {
        postSlug: Post;
        subtitle?: string | undefined;
    }[];
    slug: string;
    title: string;
    description: string;
}>

by using a function with the signature

string -> Option<Post>

I'm wondering if there're some good workarounds using sequence or something, but I can't figure it out because the field is very deep in the structure.

[dawnchan030920]

Here's the workaround solution

  pipe(
    O.Do,
    O.bind("series", () => getSeriesBySlug(slug)),
    O.bind("posts", ({ series }) =>
      pipe(
        series.posts,
        A.traverse(O.Applicative)((post) =>
          pipe(
            getPostBySlug(post.post),
            O.map((innerPost) => ({ ...post, post: innerPost }))
          )
        )
      )
    ),
    O.map(({ series, posts }) => ({
      ...series,
      posts,
    }))
  );

But it's verbose and it forces the naming of some fields, which is not good for extending