Iterate through an Elm list and compare each element against all the others

KeepInList.elm

{--
  Iterate through a list and compare each element to all the others to decide what to keep
  
  Run at http://elm-lang.org:1234/try
--}

import Html exposing (text, div, br)
import String exposing (..)

initial = ["a", "ab", "c", "cdb", "cd"]
isChild i j = String.startsWith i j && not (i == j)
hasParentIn item list = List.any (\i -> isChild i item) list
parents = List.filter (\i -> not (hasParentIn i initial)) initial

main = div [] [
  "initial: " ++ toString initial |> text, br[][],
  "parents: " ++ toString parents |> text, br[][],
  "isChild a ab: " ++ toString (isChild "a" "ab") |> text, br[][],
  "isChild ab a: " ++ toString (isChild "ab" "a") |> text, br[][],
  "isChild a a: " ++ toString (isChild "a" "a") |> text, br[][],
  "hasParentIn ab initial: " ++ toString (hasParentIn "ab" initial) |> text, br[][],
  "hasParentIn b initial: " ++ toString (hasParentIn "b" initial) |> text, br[][]
  ]

{--
Should see the following output:
  
initial: ["a","ab","c","cdb","cd"]
parents: ["a","c"]
isChild a ab: True
isChild ab a: False
isChild a a: False
hasParentIn ab initial: True
hasParentIn b initial: False
--}