elm

问题 How can I detect that an image was failed to be load in Elm? I use img [ src "/path/to/image" ] and would like to know if the image failed to load. In plan old JavaScript I would register to onError event of img but I don't see onError in Elm. 回答1: You can use Html.Events.on to capture an image load error. You will need a Msg value to indicate that the image failed. Here I'll call that ImageError : img [ src "/path/to/image", on "error" (Json.Decode.succeed ImageError) ] [] The use of Json

问题 How can I detect that an image was failed to be load in Elm? I use img [ src "/path/to/image" ] and would like to know if the image failed to load. In plan old JavaScript I would register to onError event of img but I don't see onError in Elm. 回答1: You can use Html.Events.on to capture an image load error. You will need a Msg value to indicate that the image failed. Here I'll call that ImageError : img [ src "/path/to/image", on "error" (Json.Decode.succeed ImageError) ] [] The use of Json

问题 I would like to create some buttons whose number will vary with user actions (one per value in a list or array)). I'm able to create the buttons but not to know in update which one was pressed. For instance, in the following reduced code, how can I increment the value in data corresponding to the pressed button? module Main exposing (..) import Html exposing (..) import Html.Events exposing (..) import Array exposing (..) main = Html.program { init = init , view = view , update = update ,

问题 I am making a program that changes the rendered text on the screen to be whatever the user inputs in a text box. I think I have the model and the update part of the elm architecture correct, but I really don't understand the view portion. I'm just having trouble wrapping my head around the square bracket view functions. Anyway, I am getting this error. This div call produces: Html #(Model -> Model)# But the type annotation on view says it should be: Html #Msg#Elm But I am not sure how to

问题 I seem to be getting this error Trying to send an unsupported type through outbound port `projectRequests` port projectRequests : Signal (Maybe (Task String ())) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The specific unsupported type is: Task.Task String () The types of values that can flow through outbound ports include: Ints, Floats, Bools, Strings, Maybes, Lists, Arrays, Tuples, Json.Values, and concrete records. However this seems to be fine port orgRequests : Signal (Task

问题 I'm reaching a point where GUI coding with Backbone.js object-oriented MVC pattern is getting quite complex, and looking around at other paradigms. MDV, FRP, ECS, oh my. How does Elm compare to ClojureScript? Where do they overlap? Both are languages very different from JS that compile to JS. I understand that Elm is a functional reactive programming (FRP) language. ClojureScript isn't necessarily FRP, but you can do FRP with it. Elm compiles with Haskell and ClojureScript with the JVM, so

问题 Got a hopefully simple problem. When I receive action A in my update function, I'd like to return a task that does some stuff, then results in action B, which is received by the update function again. Its my understanding that whatever effects are returned from Update will be executed by startapp, but nothing seems to be happening. Here's a whittled down example: import StartApp exposing (start) import Effects import Task import Html exposing (..) import Html.Events exposing (..) main =

问题 I am making a simple Elm application with the following model: type alias Model = { num : Float , str : String , list : List Float , serverResponse : String } I am following the Todo-MVC example and I have a similar architecture: type Action = NoOp | ChangeNum String | ChangeStr String ... view : Model -> Html view model = ... update : Action -> Model -> Model update action model = case action of ... main : Signal Html main = Signal.map view model model : Signal Model model = Signal.foldp

问题 I am making a simple Elm application with the following model: type alias Model = { num : Float , str : String , list : List Float , serverResponse : String } I am following the Todo-MVC example and I have a similar architecture: type Action = NoOp | ChangeNum String | ChangeStr String ... view : Model -> Html view model = ... update : Action -> Model -> Model update action model = case action of ... main : Signal Html main = Signal.map view model model : Signal Model model = Signal.foldp

问题 The documentation for Elm's Random module states: A good way to get an unexpected seed is to use the current time. http://package.elm-lang.org/packages/elm-lang/core/1.1.0/Random I don't see however a good example of how to perform such initialization logic in FRP application. What signal should I react to? How to do this with a minimum of code and maximum of clarity. 回答1: There are different ways to do this. Each has it's own benefits. I'll give you the three that I know with a similar