<* PRAGMA LL *>

The essence of a FeedbackVBT are its normal and excited methods. The normal method is intended for giving permanent feedback, whereas the excited method is used for displaying transitory feedback (e.g., while a button is pressed). In addition, a feedback maintains a {\it state} flag to distinguish between an ``on'' and ``off'' state (e.g., for use by a BooleanVBT).

Clients should not invoke a FeedbackVBT's normal and excited methods directly. Instead, use the procedures Normal and Excited in this interface. The state of a FeedbackVBT is set using the SetState procedure; it is queried using the procedure GetState.

The default normal and excited methods are no-ops. A FeedbackVBT by itself is not very useful; subtypes are expected to override these methods with something useful. Also, VBTkit switches that use FeedbackVBTs assume that the FeedbackVBT is a multi-filter, not simply a filter.

INTERFACE FeedbackVBT;

IMPORT Filter, VBT;

TYPE
  T <: Public;
  Public = Filter.T OBJECT
           METHODS
             <* LL <= VBT.mu *>
             init (ch: VBT.T): T;
             <* LL = VBT.mu *>
             normal  ();
             excited ();
           END;

PROCEDURE Normal (v: T);
<* LL.sup = VBT.mu *>

Invoke v's normal method.

PROCEDURE Excited (v: T);
<* LL.sup = VBT.mu *>

Invoke v's excited method.

PROCEDURE SetState (v: T; state: BOOLEAN);
<* LL.sup = VBT.mu *>

Record the state and then invoke whichever of v's methods, normal or excited, was most recently invoked. If neither method has ever been invoked, the normal method is invoked.

PROCEDURE GetState (v: T): BOOLEAN;
<* LL.sup = VBT.mu *>

Return the value of the most recent call to SetState. The initial state is FALSE.

END FeedbackVBT.