updatefunc.elm

type FilterMsg
    = UpdateTitleFilter String
    | UpdateDescriptionFilter String
    | UpdateTagFilter String

type Msg 
    = Filter FilterMsg
    | DoSomethingElse
    | DoAnotherThing


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model = 
    case msg of
        Filter subMsg ->
            updateFilter subMsg model
        DoSomethingElse ->
            -- ...
        DoAnotherThing ->
            -- ...
        

updateFilter : FilterMsg -> Model -> ( Model, Cmd Msg )
updateFilter msg model =
    let
        setFilters m =
            { m | filters = 
                createFilters m.currentTitleSearchField
                    m.currentDescriptionSearchField
                    m.currentFilteredTags 
            }
        addTag tag =
            { model | currentFilteredTags = tag :: model.currentFilteredTags }
        removeTag tag =
            { model | currentFilteredTags = List.filter (\t -> t /= tag) model.currentFilteredTags }
    in
        case msg of
            UpdateTitleFilter titleSearch ->
                ( setFilters { model | currentTitleSearchField = titleSearch }, Cmd.none )

            UpdateDescriptionFilter descSearch ->
                ( setFilters { model | currentDescriptionSearchField = descSearch } , Cmd.none )

            UpdateTagFilter tagSearch ->
                ( { model | currentTagSearchField = tagSearch }, Cmd.none )

            SubmitTagFilter ->
                ( setFilters <| addTag model.currentTagSearchField, Cmd.none )

            AddTagFilter tag ->
                ( setFilters <| addTag tag, Cmd.none )

            RemoveTagFilter tag ->
                ( setFilters <| removeTag tag, Cmd.none )