golang小白一枚,正在不断学习积累知识,现将学习到的知识记录一下,也是将我的所得分享给大家!而今天这篇文章《当参数与工作示例相同时,为什么 Elm 不会编译此 JSON 数据示例的 Http 请
golang小白一枚,正在不断学习积累知识,现将学习到的知识记录一下,也是将我的所得分享给大家!而今天这篇文章《当参数与工作示例相同时,为什么 Elm 不会编译此 JSON 数据示例的 Http 请求?》带大家来了解一下##content_title##,希望对大家的知识积累有所帮助,从而弥补自己的不足,助力实战开发!
我正在研究一个基本的解码 json elm 示例以进行练习,但无法找出 elm 编译错误。我也很困惑为什么它在 ellie 中运行(即使用远程 json url),但在使用 elm v 19.0 本地编译时却不能运行(仅供参考)。
目标是进行一个简单的调用以从 Go 服务器获取 json,但仅编译我从解码 json 的文档中获得的示例 elm 并不起作用,所以我们在这里。
module helloworld exposing (..)
import browser
import html exposing (..)
import html.attributes exposing (..)
import html.events exposing (..)
import http
import json.decode exposing (decoder, field, string)
-- main
main =
browser.element
{ init = init
, update = update
, subscriptions = subscriptions
, view = view
}
-- model
type model
= failure
| loading
| success string
init : () -> (model, cmd msg)
init _ =
(loading, getrandomcatgif)
-- update
type msg
= moreplease
| gotgif (result http.error string)
update : msg -> model -> (model, cmd msg)
update msg model =
case msg of
moreplease ->
(loading, getrandomcatgif)
gotgif result ->
case result of
ok url ->
(success url, cmd.none)
err _ ->
(failure, cmd.none)
-- subscriptions
subscriptions : model -> sub msg
subscriptions model =
sub.none
-- view
view : model -> html msg
view model =
div []
[ h2 [] [ text "random cats" ]
, viewgif model
]
viewgif : model -> html msg
viewgif model =
case model of
failure ->
div []
[ text "i could not load a random cat for some reason. "
, button [ onclick moreplease ] [ text "try again!" ]
]
loading ->
text "loading..."
success url ->
div []
[ button [ onclick moreplease, style "display" "block" ] [ text "more please!" ]
, img [ src url ] []
]
-- http
getrandomcatgif : cmd msg
getrandomcatgif =
http.get
{ url = "http://127.0.0.1:8080/test"
, expect = http.expectjson gotgif gifdecoder
}
gifdecoder : decoder string
gifdecoder =
field "data" (field "image_url" string)
现在是 go 服务器
// write json back to elm call
package main
import (
"fmt"
"log"
"net/http"
"os"
"GitHub.com/gorilla/schema"
)
type todo struct {
title string
description string
}
func main() {
http.handlefunc("/test", test)
http.listenandserve(getport(), nil)
}
func getport() string {
p := os.getenv("port")
if p != "" {
return ":" + p
}
return ":8080"
}
func test(w http.responsewriter, r *http.request) {
if r.method == "get" {
//allow cors here by * or specific origin
w.header().set("access-control-allow-origin", "*")
// say hi
fmt.fprintf(w, "hello from go"+"\n")
} else {
//allow cors here by * or specific origin
w.header().set("access-control-allow-origin", "*")
todo := readfORM(r)
fmt.fprintf(w, "updated todo to"+todo.title+"\n")
}
}
func readform(r *http.request) *todo {
r.parseform()
todo := new(todo)
decoder := schema.newdecoder()
decodeerr := decoder.decode(todo, r.postform)
if decodeerr != nil {
log.printf("error mapping parsed form data to struct : ", decodeerr)
}
return todo
}
最后是 elm 错误 elm make ./src/helloworld.elm
Detected problems in 1 module.
-- TYPE MISMATCH -------------------------------------------- src/HelloWorld.elm
Something is off with the body of the `getRandomCatGif` definition:
110|> Http.get
111|> { url = "http://127.0.0.1:8080/test"
112|> , expect = Http.expectJson GotGif gifDecoder
113|> }
This `get` call produces:
Decoder a -> Http.Request a
But the type annotation on `getRandomCatGif` says it should be:
Cmd Msg
-- TYPE MISMATCH -------------------------------------------- src/HelloWorld.elm
The 1st argument to `get` is not what I expect:
110| Http.get
111|> { url = "http://127.0.0.1:8080/test"
112|> , expect = Http.expectJson GotGif gifDecoder
113|> }
This argument is a record of type:
{ expect : b, url : String }
But `get` needs the 1st argument to be:
String
-- TYPE MISMATCH -------------------------------------------- src/HelloWorld.elm
The 1st argument to `expectJson` is not what I expect:
112| , expect = Http.expectJson GotGif gifDecoder
^^^^^^
This `GotGif` value is a:
Result Http.Error String -> Msg
But `expectJson` needs the 1st argument to be:
Decoder a
-- TOO MANY ARGS -------------------------------------------- src/HelloWorld.elm
The `expectJson` function expects 1 argument, but it got 2 instead.
112| , expect = Http.expectJson GotGif gifDecoder
^^^^^^^^^^^^^^^
Are there any missing commas? Or missing parentheses?
看起来您已经安装了 elm/http
模块的 1.0.0 版,而该示例需要 elm/http
2.0.0 版。我可以使用此包的 1.0.0 版本重现您的错误,但使用 2.0.0 版本可以成功编译代码。
编辑 elm.json
文件,将 elm/http
的版本更改为 2.0.0
并尝试再次运行 elm make ...
。
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本文标题: 当参数与工作示例相同时,为什么 Elm 不会编译此 JSON 数据示例的 HTTP 请求?
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