use ;
/// Marker for goal state.
///
/// This is used for referential param values, where an item param value is
/// dependent on the state of a predecessor's state.
///
/// A `Goal<Item::State>` is set to `Some` whenever an item's goal state
/// is discovered. enabling a subsequent successor's params to access that value
/// when the successor's goal state function is run.
///
/// Note: A successor's goal state is dependent on the predecessor's goal
/// state, which should be in sync with its current state after
/// `ApplyFns::exec` has been executed.
;