Making a query parser fail

Learn
1

Can I somehow make a query parser fail instead of returning maybes like it does for path segments?

type Route
    = VerifyEmail String

routeParser : Parser (Maybe Route -> a) a
routeParser =
    let
        toRoute mode oobCode =
            case mode of
                "verifyEmail" ->
                    Just <| VerifyEmail oobCode

                _ ->
                    Nothing
    in
    Parser.top
        <?> Query.map2 (Maybe.map2 toRoute) (Query.string "mode") (Query.string "oobCode")
        |> Parser.map (Maybe.andThen identity)

Something that would turn

routeParser : Parser (Maybe Route -> a) a

into

routeParser : Parser (Route -> a) a

It seems Parser.Query.string should be called Parser.Query.maybeString if the presence of the query param is optional?

2

It doesn’t look like it, as there is no fail operator in the API. You might have to change:

and reject the route based on the Maybe after it has been parsed. Not ideal…

3

Yeah, that’s what I ended up doing. I guess one could use elm/parser for more customisability.

4

“There’s no way to make a parser fail.”

Have you seen Parser.problem?

Edit: Oh, query parsers. Maybe problem needs to be exposed by them.

5

You’re referring to problem in elm/parser? I was looking for something in the elm/url package.

Edit: Sorry didn’t see your edit.

6

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