Ui.State.State

data State = State {
    -- | The project name is used as the namespace of automatically created
    -- IDs, so each project can import other projects without clashes.  The
    -- save file is also derived from the project name.
    state_project :: Id.Namespace
    , state_project_dir :: String
    , state_views :: Map.Map ViewId Block.View
    , state_blocks :: Map.Map BlockId Block.Block
    -- | Track data also gets a symbol table.  This is so that I can
    -- efficiently compare a track for identity, and also so I can
    -- change it here and all of its occurrances change.
    , state_tracks :: Map.Map TrackId Track.Track
    , state_rulers :: Map.Map RulerId Ruler.Ruler

    -- | This maps the midi instruments used in this State to their Addrs.
    , state_midi_config :: Instrument.Config
    -- | Automatically created pitch tracks will have this scale.  MIDI thru
    -- will also use it when a scale can't be derived from focus.
    , state_project_scale :: Pitch.ScaleId
    } deriving (Read, Show, Generics.Typeable)

IDs enforce sharing and enable aliasing, effectively recovering pointer semantics.