General workflow-management

Flow.elm

module Flow exposing (Flow(..), map, withDefault, mapDefault, view, update)

import Html


type Flow state
    = NotRunning
    | Running state


map : (state -> state') -> Flow state -> Flow state'
map f flow =
    case flow of
        NotRunning ->
            NotRunning

        Running state ->
            Running <| f state


withDefault : state -> Flow state -> state
withDefault default flow =
    case flow of
        NotRunning ->
            default

        Running state ->
            state


mapDefault : state' -> (state -> state') -> Flow state -> state'
mapDefault default fn flow =
    map fn flow
        |> withDefault default


view : (state -> Html.Html msg) -> Flow state -> Html.Html msg
view viewFn flow =
    mapDefault (Html.text "") viewFn flow


update : (state -> ( Flow state, Cmd msg )) -> Flow state -> ( Flow state, Cmd msg)
update fn flow =
    mapDefault ( flow, Cmd.none ) fn flow

Nice, but what is the Irn module?