ELM QueryString 解析器无法编译

我真的很想学习一些 ELM，但是我的思想在查询解析时崩溃了，我的想法是创建一个函数来按名称获取查询字符串值，例如：给定一个查询字符串?name=Neuber像这样的函数getParam "name"那会返回Neuber

但它在最基本的例子中失败了，它甚至无法编译

page comes 从这里 https://package.elm-lang.org/packages/elm/url/latest/Url-Parser-Query#map

routeParser comes 从这里 https://package.elm-lang.org/packages/elm/url/latest/Url-Parser-Query#map2

module Main exposing (..)
-- import Url.Parser exposing (Parser, (</>), (<?>), oneOf, s)
import Url.Parser.Query exposing (int, map, map2, string)

type alias QueryParams =
  { search : Maybe String
  , page : Maybe Int
  }


routeParser : Url.Parser.Query.Parser QueryParams
routeParser = map2 QueryParams (string "search") (int "page")

page : Url.Parser.Query.Parser Int
page = map (Result.withDefault 1) (int "page")

我得到的错误

-- TYPE MISMATCH ---------------- /a/long/way/to/project/src/Main.elm

The 2nd argument to `map` is not what I expect:

15| page = map (Result.withDefault 1) (int "page")
                                       ^^^^^^^^^^
This `int` call produces:

    Url.Parser.Query.Parser (Maybe Int)

But `map` needs the 2nd argument to be:

    Url.Parser.Query.Parser (Result x number)

Hint: I always figure out the argument types from left to right. If an argument
is acceptable, I assume it is “correct” and move on. So the problem may actually
be in one of the previous arguments!

眼前的问题是int "page"将返回一个Maybe Int，但你试图将它与Result.withDefault，正如错误消息所示，它期望Result。解决这个问题的方法就是使用Maybe.withDefault反而。