Text field blanks out unexpectedly about elm-lang.org HOT 2 CLOSED

import Graphics.Input (input, button)
import Graphics.Input.Field (field, Content, noContent, defaultStyle)

-- Some utilities
mapi : (Int -> a -> b) -> [a] -> [b]
mapi f l = zipWith f [0 .. length l - 1] l

replaceAt : Int -> a -> [a] -> [a]
replaceAt i a l =
    case l of [] -> []
              x::xs -> if i == 0 then a :: xs
                       else x :: replaceAt (i-1) a xs

-- Main program
data Event = Nop | Create | Change Int Content

events = input Nop
makeButton = button events.handle
makeField = field defaultStyle events.handle

type State = [Content]

btnCreate = makeButton Create "Create"

view : State -> Element
view lst =
    let viewOne idx content =
            makeField (Change idx) "Write here!" content
            `above`
            plainText content.string
    in flow down (btnCreate :: mapi viewOne lst)

update : Event -> State -> State
update evt x =
    case evt of
      Nop -> x
      Create -> x ++ [noContent]
      Change i c -> replaceAt i c x

main = view <~ foldp update [] events.signal