Modification of Rundberget's version at (https://gist.github.com/rundis/8b5a0fd09c3eb348dfc2aa7e862436b4) to use String as a stack

Sample.elm

import SStack as Stack exposing (..)
import Html exposing (..)

reverseString : String -> String
reverseString str =
  Stack.reverse str 


main : Html.Html
main =
  reverseString "Hello World !" 
    |> Html.text

Stack.elm

module SStack where

import String

type alias SStack = String

empty : SStack
empty =
  ""


push : String -> SStack -> SStack
push tok stacks = 
  tok ++ stacks


pop : SStack -> Maybe (Char, SStack)
pop stacks = 
  String.uncons stacks


reverse : SStack -> SStack
reverse stack =
  case (pop stack) of 
    Nothing ->
      empty
    Just(x, r) -> 
      push  (reverse r) (String.fromChar x)