elm | 易学教程

Elm - producing a list of random number changing with time

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问题 I am trying to make a column of random numbers changing every second, but I get different error messages: import Random main = flow down [ asText (Random.range 0 100 (every second)) , asText (Random.range 0 100 (every second)) ] gives a parse error. What is wrong with my square bracket [ ? Parse error at (line 5, column 1): unexpected '[' expecting newline, spaces or end of input Indent Maybe? Once I indent, the example does compile but I just get <signal> instead of the actual number main =

Access Union Types outside of declaring module in Elm

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问题 Given --module 1 module Module1 exposing (Message) where type Message = Test String | Error Int --module 2 module Module2 exposing (sayTest, sayError) where import Module1 exposing (Message) sayTest : String -> Message sayTest msg = Test msg --error sayError : Int -> Message sayError code = Error code --error processMessage : Message -> String processMessage msg -> case msg of Test s -> s Error i -> toString i How do I access Test and Error from module 2? At the moment, I have to create

Redux - One vs Multiple reducers

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问题 I come from the Elm-comunity and in Elm, every application has its view, its model and its state and basically takes very similar approach, IMO, to solving problems as redux does. Anyway, I found myself struggling with the idea of multiple reducers. In Elm I am used to make a separate file for all the actions (Messages), a separate file for "react" (View), a separate one for state (Model), and a separate one for all the reducers (Update). Every possible action gets covered inside Update file

Elm debugger sidebar is too small. How to extend it?

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问题 I have long Msg and they are the same except the last part. As you can see below - i can't tell the difference: - they are actually different. I've open up the debugger with chrome and i saw this: But this doesn't work on page reload as you might expect. It reverts back to 30 ch. Question: Where are this styles kept? So that by modifying them i always have this debugger-sidebar at 70 ch. Or is there a better way to do this? Node: It would be even better if i can make it resizable instead of

学会使用函数式编程的程序员(第2部分)

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摘要： JS函数式编程入门。原文：学会使用函数式编程的程序员(第2部分) 作者：前端小智 Fundebug 经授权转载，版权归原作者所有。本系列的其他文章: 学会使用函数式编程的程序员(第1部分) 学会使用函数式编程的程序员(第3部分) 组合函数 (Function Composition) 作为程序员，我们是懒惰的。我们不想构建、测试和部署我们编写的一遍又一遍的代码。我们总是试图找出一次性完成工作的方法，以及如何重用它来做其他事情。代码重用听起来很棒，但是实现起来很难。如果代码业务性过于具体，就很难重用它。如时代码太过通用简单，又很少人使用。所以我们需要平衡两者，一种制作更小的、可重用的部件的方法，我们可以将其作为构建块来构建更复杂的功能。在函数式编程中，函数是我们的构建块。每个函数都有各自的功能，然后我们把需要的功能(函数)组合起来完成我们的需求，这种方式有点像乐高的积木，在编程中我们称为组合函数。看下以下两个函数： var add10 = function(value) { return value + 10; }; var mult5 = function(value) { return value * 5; }; 上面写法有点冗长了，我们用箭头函数改写一下： var add10 = value => value + 10; var mult5 =

How to filter out “Nothing” values from Elm Array?

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问题 I'd like to define the following function: compactAndConvertToList : Array (Maybe String) -> List String This function should remove all Nothing appearances in the given array, and convert it to List . I came up with the solution below, but it feels dirty a bit. Is there a better way to achieve this? import Graphics.Element exposing (..) import Array model : Array.Array (Maybe String) model = Array.fromList [ Just "Hello", Just "Stack", Nothing, Just "Overflow" ] compactAndConvertToList :

Array vs List in Elm

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问题 I was suprised to learn that Array and List were two different types in Elm: Array List In my case, I have a List Int of length 2,000,000 and I need about 10,000 of them but I don't know in advance which ten thousand. That will be provided by another list. In pseudo-code: x = [ 1,1,0,30,...,255,0,1 ] y = [ 1,4,7,18,36,..., 1334823 , ... 1899876 ] z = [ y[x[0]], y[x[1]], ... ] I am using pseudocode because clearly this isn't Elm syntax (it might be legal JavaScript). Can these array selections

Understanding generic union types in Elm

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问题 I'm having some trouble understanding what exactly the Html msg type is, or how it gets used. I found this line of code in VirtualDom.elm, which Html msg seems to be an alias of: type Node msg = Node This looks like a generic union type with one type parameter, msg , and one trivial case that holds no additional information. I'm wondering: How does the div function construct one of these objects? How does an object like this get used? How could an object like this get used? Is there any value

Elm http request returns NetworkError for successful requests

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问题 I have a fair amount of experience building web apps with React but want to learn Elm. I've been banging my head against an HTTP request issue for a couple days now. I'm running an Elm app at localhost:8080 and my supporting API at localhost:8081. Whenever I make an HTTP request (I've tried both GET and POST requests) I get a NetworkError. I've been looking into Elm JSON decoders and think it's possible that this is where my problem exists but I've tried sending simple strings from my server

Elm Http Request on Init

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问题 I'm pretty new to Elm, but slowly getting familiar with it. I'm doing some simple Http Requests, which are successful in every aspect (I get the data to display, etc.) For the moment I can only get my fetchData to trigger onClick, I would like to initialize this on init, but I'm having trouble wrapping my head around this. ....here is my fetchData function: fetchData : Cmd Msg fetchData = Http.get repoInfoListDecoder "http://example/api" |> Task.mapError toString |> Task.perform ErrorOccurred