so-37393864-two-dropdowns.elm

import Html exposing (..)
import Html.App exposing (program)
import Html.Events exposing (onClick, on, targetValue)
import Html.Attributes exposing (..)
import Json.Decode as Json
import String

{-
  Summary of changes since: https://gist.github.com/freakingawesome/2a021ddeaf0fb3592c4714885339ca2a
  
   - Replaced hardcoded 10 with a multiplier value that is selected in a dropdown
   - Removed `cost` field from Model in favor of a `calculateCost` function
-}

main =
  program { init = (initialModel, Cmd.none), view = view, update = update, subscriptions = always Sub.none }

initialModel =
  { month = 0
  , multiplier = 0
  , email = "[email protected]"
  }

intOption i =
  let s = toString i
  in option [value s ] [ text s ]

view : Model -> Html Msg
view model =
  Html.div []
    [ input [ placeholder "[email protected]" ] []
    , select [ on "change" (Json.map MonthChanged targetValueIntDecoder) ]
      (List.map intOption [0..12]) -- month selector
      
    , select [ on "change" (Json.map MultiplierChanged targetValueIntDecoder) ]
      (List.map intOption (List.map ((*) 10) [0..10]))
      
    , Html.span [][text (toString <| calculateCost model)]
    
    , button [ onClick Submit ] [text "Send"]
    ] 
   
targetValueIntDecoder : Json.Decoder Int
targetValueIntDecoder =
  targetValue `Json.andThen` \val ->
    case String.toInt val of
      Ok i -> Json.succeed i
      Err err -> Json.fail err

calculateCost : Model -> Int
calculateCost m =
  m.month * m.multiplier
  
type Msg
  = Submit
  | MonthChanged Int
  | MultiplierChanged Int
  
type alias Model =
  { month : Int
  , multiplier : Int
  , email : String
  }

update msg model =
  case msg of
    Submit ->
      (model, Cmd.none)
    MonthChanged month ->
      ({ model | month = month }, Cmd.none)
    MultiplierChanged multiplier ->
      ({ model | multiplier = multiplier }, Cmd.none)

thanks again :)

I had the idea to do:

actions can be Submit or Calculate
each time user change select values, it calls Calculate. When user click on the submit button it calls Submit

Then instead of having a function to manage each select, can I have an unique fonction ? This function is suppose to update model.month or model.multiplier then I thought it can be possible to do with an unique action.
For your information, my full example is here, it's a simple calculator supposed to estimate your project costs.
As you can see, I'm not really comfortable with elm and FP (and my English, sorry I'm French :)) but I really try to understand how do Elm and Haskell work (with http://learnyouahaskell.com/).