elm

问题 This question already has an answer here : trigger an Action from the Update function (1 answer) Closed 3 years ago . I've the following Action handler in my update function of Elm StartApp MUV framework. signupAlertMailbox : Signal.Mailbox String signupAlertMailbox = Signal.mailbox "" update : Action -> Model -> (Model, Effects Action) update action model = case action of Submit -> let isInputValid = Dict.foldl (\fieldName fieldState validity -> if validity then (fieldState == IsOkay) else

问题 I receive the following error after performing an HTTP post: Unable to get property 'tag' of undefined or null reference I believe the error occurs when executing the following decoder function: sourceDecoder : Decoder JsonSource sourceDecoder = Decode.map5 JsonSource ... (field "Links" providerLinksDecoder) Decoder Dependencies: providerLinksDecoder : Decoder JsonProviderLinks providerLinksDecoder = Decode.map JsonLinkFields (field "Links" <| Decode.list (Decode.lazy (\_ -> linkDecoder))) |>

问题 So I need to decode a json that contains a json array in elm . Here is my model: type alias ValidationResult = { parameter : String , errorMessage : String } type alias ErrorResponse = { validationErrors : List ValidationResult } And here is an example of the json : {"ValidationErrors": [{"Parameter": "param1","ErrorMessage": "message 1"},{"Parameter": "param2","ErrorMessage": "error message 2"}]} I've tried to create a ValidationResult decoder, like: decodeValidationResults : Decoder

问题 I want to make an HTML form that actually uses the [form] tag in ELM. None of the example online do this -- they simply put the [input] tags in a [div] instead of a [form] When I try switching my Elm app to a [form], my [input type=sumbit] tags don't seem to call back to Elm. The submit tries to leave the page and add a "?" to my url. Any hints on how to do this? WHY: I want to be a using [form], so I can use the "required" attribute on some [input] fields. This is just one part of my

问题 Currently, I have a nested component that only shows an error text. The view method receives a Model and returns Html , but the compiler complains saying that Html needs another value, so I ended up doing this: view: Model -> Html () view error = div [class "docs-section error-bar"] [ errorText error ] errorText: Model -> Html () errorText error = case error.text of Nothing -> span [][] Just value -> text value What I don't like is that I have to add the () value to the signature. Is there a

问题 I'm trying to adapt the Elm tutorial to my own little project and I'm running into trouble with the Json.Decoder that I am supplying. My code looks like this: type Msg = RetrieveComments | FetchSucceed String | FetchFail Http.Error update : Msg -> Model -> ( Model, Cmd Msg) update msg model = case msg of RetrieveComments -> (model, retrieveComments) FetchSucceed whatever -> (model, Cmd.none) FetchFail error -> (model, Cmd.none) retrieveComments : Cmd Msg retrieveComments = let url = "

问题 First some code: import Random import Window writeRandom x = lift asText (Random.range 0 x <| every second) upperLimit = 300 -- upperLimit = Window.width -- How can i use this instead? main = writeRandom upperLimit Ultimately I'm trying to get random points on the screen, but I can't figure out how to pass Window.height and Window.width to Random.range. I don't think I can 'lift' Random.range, since it already returns a signal. If I try I get a type error: Type Error: 'main' must have type

问题 It's possible to write parallel code in Elm? Elm is pure functional, so no locking is needed. Of course, I can use Javascript FFI, spawn workers here and do it on my own. But, I want more user friendly "way" of doing this. 回答1: Short answer No, not currently. But the next release (0.15) release will have new ways to handle effects inside Elm so you will need to use ports + JavaScript code less. So there may well be a way to spawn workers inside Elm in the next version. More background If you

问题 I have a list of lists of ints [[1,2,3,4],[1,2,3,4]] I want to transpose that to [[1,1],[2,2],[3,3]...] I have: transpose : List (List a) -> List (List a) transpose ll = case ll of ((x::xs)::xss) -> (x :: (List.map List.head xss)) :: transpose (xs :: (List.map List.tail xss)) otherwise -> [] but the issue is that the compiler doesn't like the head and tail operations and wants to return a Maybe type. How do I transpose a list properly in elm? 回答1: It depends... Do you want to do this

问题 In Elm I have a model with nested attributes like: model = { name = "" , disruptedFields = { advertising = { name = "Advertising" , checked = False } , travel = { name = "Travel" , checked = False } , utilities = { name = "Utilities" , checked = False } } } disruptedFields contains a list of values for checkboxes. When I click on the checkbox I send an update message to UpdateDisruptedField , which currently looks like: UpdateDisruptedField value -> let fieldCollection = model.disruptedFields