Swap part1 and part2

advanced/part2/src/Article.elm

@@ -56,64 +56,22 @@ import Viewer.Cred as Cred exposing (Cred)
 -- TYPES
 
 
-{-| An article, optionally with an article body.
-
-To see the difference between { extraInfo : a } and { extraInfo : Maybe Body },
-consider the difference between the "view individual article" page (which
-renders one article, including its body) and the "article feed" -
-which displays multiple articles, but without bodies.
-
-This definition for `Article` means we can write:
-
-viewArticle : Article Full -> Html msg
-viewFeed : List (Article Preview) -> Html msg
-
-This indicates that `viewArticle` requires an article _with a `body` present_,
-wereas `viewFeed` accepts articles with no bodies. (We could also have written
-it as `List (Article a)` to specify that feeds can accept either articles that
-have `body` present or not. Either work, given that feeds do not attempt to
-read the `body` field from articles.)
-
-This is an important distinction, because in Request.Article, the `feed`
-function produces `List (Article Preview)` because the API does not return bodies.
-Those articles are useful to the feed, but not to the individual article view.
-
--}
 type Article a
     = Article Internals a
 
 
-{-| Metadata about the article - its title, description, and so on.
 
-Importantly, this module's public API exposes a way to read this metadata, but
-not to alter it. This is read-only information!
+-- 💡 HINT: We can use these `Preview` and/or `Full` types to store information...
 
-If we find ourselves using any particular piece of metadata often,
-for example `title`, we could expose a convenience function like this:
 
-Article.title : Article a -> String
+type Preview
+    = Preview
 
-If you like, it's totally reasonable to expose a function like that for every one
-of these fields!
 
-(Okay, to be completely honest, exposing one function per field is how I prefer
-to do it, and that's how I originally wrote this module. However, I'm aware that
-this code base has become a common reference point for beginners, and I think it
-is _extremely important_ that slapping some "getters and setters" on a record
-does not become a habit for anyone who is getting started with Elm. The whole
-point of making the Article type opaque is to create guarantees through
-_selectively choosing boundaries_ around it. If you aren't selective about
-where those boundaries are, and instead expose a "getter and setter" for every
-field in the record, the result is an API with no more guarantees than if you'd
-exposed the entire record directly! It is so important to me that beginners not
-fall into the terrible "getters and setters" trap that I've exposed this
-Metadata record instead of exposing a single function for each of its fields,
-as I did originally. This record is not a bad way to do it, by any means,
-but if this seems at odds with <https://youtu.be/x1FU3e0sT1I> - now you know why!
-See commit c2640ae3abd60262cdaafe6adee3f41d84cd85c3 for how it looked before.
-)
+type Full
+    = Full
+
 
--}
 type alias Metadata =
     { description : String
     , title : String
@@ -131,14 +89,6 @@ type alias Internals =
     }
 
 
-type Preview
-    = Preview
-
-
-type Full
-    = Full Body
-
-
 
 -- INFO
 
@@ -159,8 +109,8 @@ slug (Article internals _) =
 
 
 body : Article Full -> Body
-body (Article _ (Full extraInfo)) =
-    extraInfo
+body _ =
+    "👉 TODO make this return the article's body"
 
 
 
@@ -181,8 +131,8 @@ mapAuthor transform (Article info extras) =
 
 
 fromPreview : Body -> Article Preview -> Article Full
-fromPreview newBody (Article info Preview) =
-    Article info (Full newBody)
+fromPreview _ _ =
+    "👉 TODO convert from an Article Preview to an Article Full"
 
 
 
@@ -200,7 +150,16 @@ fullDecoder : Maybe Cred -> Decoder (Article Full)
 fullDecoder maybeCred =
     Decode.succeed Article
         |> custom (internalsDecoder maybeCred)
-        |> required "body" (Decode.map Full Body.decoder)
+        |> required "body" "👉 TODO use `Body.decoder` (which is a `Decoder Body`) to decode the body into this Article Full"
+
+
+
+{- If you're unfamiliar with Decode Pipeline, here's how ☝️ would look without it:
+
+   Decode.map2 Article
+       (internalsDecoder maybeCred)
+       (Decode.field "body" "use `Body.decoder` (which is a `Decoder Body`) to decode the body into this Article Full")
+-}
 
 
 internalsDecoder : Maybe Cred -> Decoder Internals