An action pre-condition object. Each condition of an action is represented by a subclass of this class.

class PreCondition :   object

Superclass Tree   (in declaration order)


Subclass Tree  


Global Objects  

actorDirectlyInRoom  actorReadyToEnterNestedRoom  actorStanding  actorTravelReady  canTalkToObj  dropDestinationIsOuterRoom  nearbyAttachableCond  objAudible  objBurning  objClosed  objEmpty  objHeld  objNotAttached  objNotWorn  objSmellable  objUnlocked  objVisible  roomToHoldObj 

Summary of Properties  


Summary of Methods  

checkPreCondition  verifyPreCondition 



Precondition execution order. When we execute preconditions for a given action, we'll sort the list of all applicable preconditions in ascending execution order.

For the most part, the relative order of two preconditions is arbitrary. In some unusual cases, though, the order is important, such as when applying one precondition can destroy the conditions that the other would try to create but not vice versa. When the order doesn't matter, this can be left at the default setting.


checkPreCondition (obj, allowImplicit)precond.t[36]

Check the condition on the given object (which may be nil, if this condition doesn't apply specifically to one of the objects in the command). If it is possible to meet the condition with an implicit command, and allowImplicit is true, try to execute the command. If the condition cannot be met, report a failure and use 'exit' to terminate the command.

If allowImplicit is nil, an implicit command may not be attempted. In this case, if the condition is not met, we must simply report a failure and use 'exit' to terminate the command.

verifyPreCondition (obj)precond.t[54]
Verify the condition. This is called during the object verification step so that the pre-condition can add verifications of its own. This can be used, for example, to add likelihood to objects that already meet the condition. Note that it is generally not desirable to report illogical for conditions that checkPreCondition() enforces, because doing so will prevent checkPreCondition() from ever being reached and thus will prevent checkPreCondition() from attempting to carry out implicit actions to meet the condition.

'obj' is the object being checked. Note that because this is called during verification, the explicitly passed-in object must be used in the check rather than the current object in the global current action.

TADS 3 Library Manual
Generated on 5/16/2013 from TADS version 3.1.3