The definition of the base class for Zeus algorithms and views.

INTERFACE ZeusClass;

IMPORT Rd, VBT, Wr;

EXCEPTION Error(TEXT);

TYPE
  T <: Public;
  Private <: VBT.T;
  Public = Private OBJECT
           METHODS
             (* LL = VBT.mu *)
             install    ();
             delete     ();
             snapshot   (wr: Wr.T) RAISES {Error};
             restore    (rd: Rd.T) RAISES {Error};
             config     (state: StateChange; object: T);
             reactivity (on: BOOLEAN);
           END;

TYPE StateChange = {ViewAttached, ViewDetached, LockedBy, UnlockedBy};

Special note: install should NOT put windows on the screen. The restore method will be called immediately after install, and will take care of putting up the windows.

delete(v) is called to delete from the WM all windows v has installed. This procedure will never be called more than once; if it is called, it is guaranteed that the install method was previously invoked.

Note that there are two ways for v to be deleted: by the user issuing a delete command to the WM, or by invoking v's delete method (in response to some command in the control panel). Thus any necessary cleanup should be performed by the thread that install() forks, rather than by the delete() method.

snapshot(v, wr) is called to snapshot the state of v as exactly one s-expression written into the supplied writer. The state should include a description and location of any windows that v installs, any data it has gotten from the user, and so on.

restore(v, rd) is passed a reader positioned just before the s-expression that was written by v's snapshot method. The restore method should restore the static state of v from this description. This method and v's snapshot method should be inverses.

A view's restore method should restore the positions of windows. The same is true for the restore method of an algorithm that installs windows.

If the restore method is passed rd = NIL as an argument, it should restore the alg or view to its initial state, which in the case of a view means putting the windows on the screen in some default position.

config(v, whatChanged, instigator) is called by Zeus whenever Zeus's configuration changes. A configuration change happens when a view is attached or detached, or a view has acquired or released the edit lock.

reactivity(v, on) is called by ZeusPanel to enable (on=TRUE) or disable (on=FALSE) feedback events. It will be called when the algorithm pauses.

If a subtype overrides one or more of the default methods, the overriding method should call the method of the supertype.

END ZeusClass.