split everything into modules

elm/Post.elm

module Post where
import Date (Date)
import Util.Html (viewDate)
import Html (..)
type alias Post = { title:String, content:String, created:Date }
view : Date -> Post -> Html
view ref post = div [] [
                 h3 [] [text post.title],
                 p [] [text post.content],
                 span [] [text "Written ", viewDate ref post.created]
                ]

elm/Stream.elm

import String
import PrettyDate (prettyDate)
type alias Post = { title:String, content:String, created:Date }
import Post
import Post (Post)
date s = case (Date.fromString s) of
    Ok  d -> d
         {title = "Ancient history", content = "Teenage angst!!!!", created = date "2009-06-07T02:54:29"}
        ]
referenceDate = date "2015-03-01T14:09"
viewDate : Date -> Html
viewDate d = let dateString = prettyDate referenceDate d
                 isoDate = formatDate "%Y-%m-%dT%H:%M:%SZ" d
             in time [Attr.title isoDate, Attr.datetime isoDate] [(text dateString)]
viewPost : Post -> Html
viewPost post = div [] [
                 h3 [] [text post.title],
                 p [] [text post.content],
                 span [] [text "Written ", viewDate post.created]
                ]
flipOrder : Order -> Order
flipOrder o = case o of
                LT -> GT
sortByDate = List.sortBy (.created >> Date.toTime)
sortByDateReverse = List.sortWith (flipCompare <| compareBy (.created >> Date.toTime))
main = div [] (List.map viewPost (sortByDateReverse posts))
referenceDate = date "2015-03-01T14:09"
main = div [] (List.map (Post.view referenceDate) (sortByDateReverse posts))

elm/Util/Html.elm

module Util.Html where
import Date (Date)
import Html (..)
import Html.Attributes as Attr
import FormatDate (formatDate)
import PrettyDate (prettyDate)
viewDate : Date -> Date -> Html
viewDate ref d = let dateString = prettyDate ref d
                     isoDate = formatDate "%Y-%m-%dT%H:%M:%SZ" d
                 in time [Attr.title isoDate, Attr.datetime isoDate] [(text dateString)]