elm

I have a <select> HTML element with 3 options and a <p> element. In the <p> element I want to print index of the currently selected item in <select> . E.g. if I select the first option, it should print 0, if I select the second option, it should print 1, and so on. How do I proceed from the minimal code, which is given below? import Html as H exposing (Html) import Maybe import Signal as S exposing (Address, (<~)) type alias Model = { selected : Maybe Int } model = { selected = Nothing } type Action = NoOp | Select Int update action model = case action of NoOp -> model Select n -> { model |

I have encountered that in the guide: viewValidation : Model -> Html msg viewValidation model = let (color, message) = if model.password == model.passwordAgain then ("green", "OK") else ("red", "Passwords do not match!") in div [ style [("color", color)] ] [ text message ] So this is a function, which takes the Model . Html msg usually looks to me like we are calling the function Html with the argument msg . msg doesn't seem to play any role in any other part of the viewValidation function, though. So what does it mean and what is it for in this case? marcosh Html Msg is just a type parameter,

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 for a user to define a type like this, or is Html msg just a magical type to support the Elm compiler

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 be done in List or Array or both? List is a linked list which provides O(n) lookup time based on index

I've used types before but don't know what an opaque type is. I've seen it mentioned as well. Is it better to expose an opaque type than a type alias? Nathan Let’s answer this question by first looking at type aliases: A type alias is fully transparent. This means that any other module importing it will have full access to its inner workings. Let’s say we’ve got a User module exposing a User type: module User exposing User type alias User = { userName : String , age : Int } Anyone importing User can manipulate the data, e.g. newUser = { oldUser | age = 25 } . Or do someUser = User "Bill" 27 .