gpt.md

Input:

headingsDecoder : String -> String -> BackendTask FatalError (Entry Data)
headingsDecoder slug rawBody =
    let
        findThis : Result String (List Block) -> BackendTask FatalError (Entry Data)
        findThis =
            Debug.todo "REPLACE"
    in
    rawBody
        |> Markdown.Parser.parse
        |> Result.mapError (\_ -> "Markdown parsing error")
        |> findThis

Available Elm functions (you must use some of these but not all of them will be needed or useful for the solution):

• gatherHeadings : List Block -> List ( Block.HeadingLevel, List Inline )
• nameAndTopLevel : String -> List ( Block.HeadingLevel, List Block.Inline ) -> Result String (Entry Data)
• FatalError.fromString : String -> FatalError
• BackendTask.mapError : (error -> errorMapped) -> BackendTask error value -> BackendTask errorMapped value
• BackendTask.fromResult : Result error value -> BackendTask error value
• BackendTask.fail : error -> BackendTask error a
• Result.map : (a -> value) -> Result x a -> Result x value
• Result.andThen : (a -> Result x b) -> Result x a -> Result x b
• Result.mapError : (x -> y) -> Result x a -> Result y a
• Result.withDefault : a -> Result x a -> a
• Result.toMaybe : Result x a -> Maybe a
• Result.fromMaybe : x -> Maybe a -> Result x a

---

GPT Response

We can add a type annotation in our let binding to make our target type that we are trying to fill in explicit.

headingsDecoder : String -> String -> BackendTask FatalError (Entry Data)
headingsDecoder slug rawBody =
    let
        findThis : Result String (List Block) -> BackendTask FatalError (Entry Data)
        findThis =
            Debug.todo "REPLACE"
    in
    rawBody
        |> Markdown.Parser.parse
        |> Result.mapError (\_ -> "Markdown parsing error")
        |> findThis

Step 2:

Result.andThen ALMOST gives us the desired type (Result String (List Block) -> BackendTask FatalError (Entry Data)), but it takes a function of type List Block -> Result FatalError (Entry Data) instead of List Block -> BackendTask FatalError (Entry Data). As an intermediary step, we create a let binding with a type annotation, and add a Debug.todo to fill in that would turn it into the desired type.

headingsDecoder : String -> String -> BackendTask FatalError (Entry Data)
headingsDecoder slug rawBody =
    let
        processListBlock : List Block -> Result FatalError (Entry Data)
        processListBlock =
            Debug.todo "REPLACE"

        findThis : Result String (List Block) -> BackendTask FatalError (Entry Data)
        findThis =
            Result.andThen processListBlock
    in
    rawBody
        |> Markdown.Parser.parse
        |> Result.mapError (\_ -> "Markdown parsing error")
        |> findThis

Step 3:

Now we can fill in the processListBlock helper function:

headingsDecoder : String -> String -> BackendTask FatalError (Entry Data)
headingsDecoder slug rawBody =
    let
        processListBlock : List Block -> Result FatalError (Entry Data)
        processListBlock listBlock =
            listBlock
                |> gatherHeadings
                |> nameAndTopLevel slug

        findThis : Result String (List Block) -> BackendTask FatalError (Entry Data)
        findThis =
            Result.andThen processListBlock
    in
    rawBody
        |> Markdown.Parser.parse
        |> Result.mapError (\_ -> "Markdown parsing error")
        |> findThis

Step 4:

Now, we need to convert the Result FatalError (Entry Data) from findThis into a BackendTask FatalError (Entry Data) using BackendTask.fromResult.

headingsDecoder : String -> String -> BackendTask FatalError (Entry Data)
headingsDecoder slug rawBody =
    let
        processListBlock : List Block -> Result FatalError (Entry Data)
        processListBlock listBlock =
            listBlock
                |> gatherHeadings
                |> nameAndTopLevel slug

        findThis : Result String (List Block) -> BackendTask FatalError (Entry Data)
        findThis result =
            result
                |> Result.andThen processListBlock
                |> BackendTask.fromResult
    in
    rawBody
        |> Markdown.Parser.parse
        |> Result.mapError (\_ -> "Markdown parsing error")
        |> findThis

Finally, we have arrived at the solution without any Debug.todo calls.