Elm-lang app that needs speed boost

app.elm

import Html exposing (Html)
import Debug
import Array exposing (Array)
import Html.Attributes as HtmlA -- exposing (..)
import Html.Events as HtmlE --exposing (on, onClick, targetChecked)
import Signal exposing (Address)
import StartApp.Simple as StartApp


main =
  StartApp.start { model = initialModel, view = view, update = update }

-- MODEL

type alias Model = Array (Array Bool)

w = 400
h = 400

initialModel : Model
initialModel = Array.repeat w <| Array.repeat h False


-- UPDATE

type Action
  = Hi Int Int

update : Action -> Model -> Model
update action model =
  case action of
    Hi rowNo colNo ->
      let
        row =
          Array.get rowNo model
          |> Maybe.withDefault (Debug.crash "derp")
        newval =
          if Array.get colNo row == Just True
            then False
            else True
        newrow = Array.set colNo newval row
      in
        Array.set rowNo newrow model

-- VIEW
view : Address Action -> Model -> Html
view address model =
  Html.table
    [ HtmlA.style [("border-collapse", "collapse")] ]
    ( model
      |> Array.indexedMap (rowHtml address)
      |> Array.toList
    )

rowHtml : Address Action -> Int -> Array Bool -> Html
rowHtml address rowNo row = 
  Html.tr
    []
    ( row
      |> Array.indexedMap (cellHtml address rowNo)
      |> Array.toList
    )

cellHtml : Address Action -> Int -> Int -> Bool -> Html
cellHtml address rowNo colNo cell =
  let
    bg =
      if cell
         then "blue"
         else "white"
  in
    Html.td
      [ HtmlE.onClick address (Hi rowNo colNo)
      , HtmlA.style [("background", bg)] ]
      [ Html.text "*" ]