Elm: My Custom Elm Decimal to Hex Converter for CSS 6 digit RGB Colors

elm_decimaltoHexRGB_converter.elm

import Html exposing (text, div)
import Html.Attributes as Attributes exposing(style)
import List
import Array
import String

getValue: Int -> Array.Array Char -> Char
getValue = 
         (\idx array ->
                (Maybe.withDefault '?' (Array.get idx array)))
             
 
toHex: Int -> String
toHex dec =

 let
   
   digitsA = Array.fromList (String.toList "0123456789ABCDEF")
   x =   dec % 16
   rest = dec // 16
 in
     if rest == 0 then
         String.fromChar (getValue x digitsA)
     else
       (toHex rest) ++ String.fromChar (getValue x digitsA)

makeHex6: Int -> String
makeHex6  num =
       let  
          unformatted_hex =  toHex num
          len = String.length unformatted_hex
       in
          case len of
         6 ->
            "#" ++ unformatted_hex
         
         5 ->
            "#0" ++ unformatted_hex

         4 ->    
            "#00" ++ unformatted_hex
         
         3 ->    
            "#000" ++ unformatted_hex

         2 ->    
            "#0000" ++ unformatted_hex

         1 ->    
            "#00000" ++ unformatted_hex          
         _ ->
            "Not a valid number"
            
            
main =
        div[Attributes.style [("background-color", makeHex6 500), ("color", "white")] ] [text (makeHex6 500)]