An Introduction to Elm Series: Solution to ‘Time’ example

 in Elm by

In http://guide.elm-lang.org/architecture/effects/time.html, we are given an application that resembles a clock and we are asked to add a button to pause it and add additional hands.

What we did in the following code is:

  • We created a normal clock that shows the time in UTC
  • A toggle button that pauses/resumes it was added
  • We added the second, minute and hour hands. Which we gave them different lengths and colors
  • We created utilities to convert time to angle in degrees both for minutes/seconds and for hours
  • A new function that adds the leading zero to values when we print the time in digital format was created
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import Html exposing (Html, br, div, button)
import Html.Events exposing (onClick)
import Html.App as Html
import Svg exposing (..)
import Svg.Attributes exposing (..)
import Time exposing (Time, second)
 
 
 
main =
  Html.program
    { init = init
    , view = view
    , update = update
    , subscriptions = subscriptions
    }
 
 
 
-- MODEL
 
 
type alias Model =
  { time : Time
  , state : Bool
  }
 
 
init : (Model, Cmd Msg)
init =
  (Model 0 True, Cmd.none)
 
 
 
-- UPDATE
 
 
type Msg
  = Tick Time
  | Toggle
 
 
update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    Tick newTime ->
      ({ model | time = newTime }, Cmd.none)
 
    Toggle ->
      (toggleState model, Cmd.none)
 
 
-- UTILITIES
toggleState : Model -> Model
toggleState model =
  {model | state = not(model.state)}
 
printWithLeadingZero : Int -> String
printWithLeadingZero number =
  if number < 10 then
    "0" ++ (toString number)
  else
    toString number
 
degressCorrection : Float
degressCorrection =
  90.0 -- The correction we must do on our analog clock to show 12 pointing up instead to the right
 
degressForHour : Float
degressForHour =
  360.0 / 12.0 -- We divide the total degrees of a full circle by the full hours of the day to get the degrees per hour
 
degreesForMinute : Float
degreesForMinute =
  360.0 / 60.0 -- We divide the total degrees of a full circle by the full minutes of the hour to get the degrees per minute
 
convertToDegrees : Int -> Float -> Float
convertToDegrees value degreesPerPoint =
  degrees (((toFloat value) * degreesPerPoint) - degressCorrection)
 
minutesToDegrees : Int -> Float
minutesToDegrees minutes =
  convertToDegrees minutes degreesForMinute
 
hoursToDegrees : Int -> Float
hoursToDegrees hours =
  convertToDegrees hours degressForHour
 
-- SUBSCRIPTIONS
 
 
subscriptions : Model -> Sub Msg
subscriptions model =
  case model.state of
    True ->
      Time.every second Tick
    False ->
      Sub.none
 
 
 
-- VIEW
 
 
view : Model -> Html Msg
view model =
  let
 
 
    second' =
        Time.inSeconds model.time
 
    secondOfMinute =
        truncate second' `rem` 60
 
    secondAngle =
      minutesToDegrees secondOfMinute
 
    secondHandX =
      toString (50 + 40 * cos secondAngle)
 
    secondHandY =
      toString (50 + 40 * sin secondAngle)
 
    minute' =
      Time.inMinutes model.time
 
    minuteOfHour =
      truncate minute' `rem` 60
 
    minuteAngle =
      minutesToDegrees minuteOfHour
 
    minuteHandX =
      toString (50 + 35 * cos minuteAngle)
 
    minuteHandY =
      toString (50 +35 * sin minuteAngle)
 
    hour' =
      Time.inHours model.time
 
    hourOfDay =
      truncate hour' `rem` 24
 
    hourAngle =
      hoursToDegrees hourOfDay
 
    hourHandX =
      toString (50 + 30 * cos hourAngle)
 
    hourHandY =
      toString (50 + 30 * sin hourAngle)
 
    currentTime =
      (printWithLeadingZero hourOfDay) ++ ":" ++ (printWithLeadingZero minuteOfHour) ++ ":" ++ (printWithLeadingZero secondOfMinute)
 
  in
    div []
      [ div [] [text currentTime]
      , svg [ viewBox "0 0 100 100", width "300px" ]
        [ circle [ cx "50", cy "50", r "45", fill "#0B79CE" ] []
        , line [ x1 "50", y1 "50", x2 secondHandX, y2 secondHandY, stroke "#ee0000" ] []
        , line [ x1 "50", y1 "50", x2 minuteHandX, y2 minuteHandY, stroke "#0000ee" ] []
        , line [ x1 "50", y1 "50", x2 hourHandX, y2 hourHandY, stroke "#023963" ] []
       ; ]
      , br [] []
      , button [onClick Toggle] [text "Toggle Clock Status"]
     ; ]

You can download the solution from here [download id=”1816″]

 

This post is also available in: Greek

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