Question

I am learning Erlang and I am trying to create a very sample blog program. However my mind currently is trapped in the OO world (var p = new Post(); p.Title = “”; p.Save();). I would like to understand some basic thinkings in Erlang. Instead of creating Post object what I should do in terms of data structure (p.Title, p.DateCreated, p.Body)? Should I be using tuple? I would like to understand the recommended way in doing such things (in both Erlang specific and or Functional Programming specific). Or is what I am doing fundamentally wrong in either Erlang or FP?

Requirement (in OO terms, not sure how to explain in FP terms yet ^_^):

1. create Post object (id, title, date_created, body, IList)
2. create Comment object (id, post_id, created_by (name as string), date_created)
3. one Post can have multiple comments
4. post.AddComment(Comment)

Thanks.

Updated:
I am not looking for specific way of doing OOP in Erlang unless it’s the recommended way. I am looking for standard/recommended way of doing what’s described in the question, however I am not trying to replicate OOP in Erlang.

Answer 1

I would use records:

-record(post, {title, date_created, body, comments = []}).
-record(comment, {created_by, date_created, content}).

Then if you want to use mnesia as database:

Post = #post{title = "", body = "", date_created = erlang:universaltime()},
mnesia:transaction(fun() -> mnesia:write(Post) end).

To add a comment:

Comment = #comment{created_by = "", content = "", date_created = erlang:universaltime()},
mnesia:transaction(fun() ->
    [Post] = mnesia:read(post, Title),
    PostWithNewComment = Post#post{comments = [Comment | Post#post.comments]},
    mnesia:write(PostWithNewComment)
end).

I haven’t tested the code, but this is what I would do. Also I assumed that each title is unique.