move comparison into it's own module as well

elm/Post.elm

module Post where
import Date
import Date (Date)
import Util.Html (viewDate)
import Html (..)
import Util.Compare (compareBy, flipCompare)
import Util.Html (viewDate)
type alias Post = { title:String, content:String, created:Date }
compareByDate = compareBy (.created >> Date.toTime)
compareByDateReverse = flipCompare <| compareBy (.created >> Date.toTime)
view : Date -> Post -> Html
view ref post = div [] [
                 h3 [] [text post.title],

elm/Stream.elm

         {title = "Ancient history", content = "Teenage angst!!!!", created = date "2009-06-07T02:54:29"}
        ]
flipOrder : Order -> Order
flipOrder o = case o of
                LT -> GT
                EQ -> EQ
                GT -> LT
flipCompare : (a -> a -> Order) -> a -> a -> Order
flipCompare compare' a b = flipOrder <| compare' a b
compareBy : (a -> comparable) -> a -> a -> Order
compareBy f a b = compare (f a) (f b)
sortByDate = List.sortBy (.created >> Date.toTime)
sortByDateReverse = List.sortWith (flipCompare <| compareBy (.created >> Date.toTime))
referenceDate = date "2015-03-01T14:09"
main = div [] (List.map (Post.view referenceDate) (sortByDateReverse posts))
main = div [] (List.map (Post.view referenceDate) (List.sortWith Post.compareByDateReverse posts))

elm/Util/Compare.elm

module Util.Compare where
flipOrder : Order -> Order
flipOrder o = case o of
                LT -> GT
                EQ -> EQ
                GT -> LT
flipCompare : (a -> a -> Order) -> a -> a -> Order
flipCompare compare' a b = flipOrder <| compare' a b
compareBy : (a -> comparable) -> a -> a -> Order
compareBy f a b = compare (f a) (f b)