StackTraceInfo

The StackTraceInfo class provides an author with a means of analyzing the TADS 3 stack trace facility and is especially useful for determining whether an action is involved in the call chain before the globals have been set by the library.

Proteus uses it in conjunction with the memory module to determine whether the action being evaluated is one of the diagnostic actions, at which point we bypass the normal memory requirements of topics.

To take advantage of this class simply create an instance with the new operator:

local x = new StackTraceInfo();

If we were to examine the stack produced by the command <<@purloin dagger>> in the memory.t module’s knowsTopic() method for the Actor class, we might retrieve the following stack information from our StackTraceInfo instance:

stack_ = [obj#2ec1 (T3StackInfo),obj#2ea3 (T3StackInfo),obj#2e84 (T3StackInfo),obj#2e67 (T3StackInfo),obj#2e47 (T3StackInfo),obj#2e29 (T3StackInfo),obj#2e09 (T3StackInfo),obj#2df0 (T3StackInfo),obj#2ddb (T3StackInfo),obj#2dc7 (T3StackInfo),obj#2db2 (T3StackInfo),obj#2d9f (T3StackInfo),obj#2d8a (T3StackInfo),obj#2d76 (T3StackInfo),obj#2d61 (T3StackInfo),obj#2d4e (T3StackInfo),obj#2d39 (T3StackInfo),obj#2d25 (T3StackInfo),obj#2d10 (T3StackInfo),obj#2cfd (T3StackInfo),obj#2ce8 (T3StackInfo),obj#2cd4 (T3StackInfo),obj#2c2a (T3StackInfo),obj#2c12 (T3StackInfo),obj#2c05 (T3StackInfo),obj#2bf7 (T3StackInfo),obj#2be7 (T3StackInfo),obj#2bd9 (T3StackInfo),obj#2bcc (T3StackInfo),obj#2bbe (T3StackInfo),obj#2bb1 (T3StackInfo)]

commandList = [obj#29f9 (firstCommandPhrase(commandOnly)),obj#29b3 (commandPhrase(definiteConj))]

predicateList = [obj#29a7 (predicate(PurloinObj))]

actionClassList = [PurloinObjAction]

We now know that the library is processing a PurloinObjAction, even though gAction has not yet been set. We can query the StackTraceInfo object further by sending the message hasDiagnosticAction() and determine whether this action is one of proteus’ diagnostic actions. It is.

The StackTraceInfo class provides the following attributes and methods:

commandList

This is a list of any CommandPhrase class objects found in the stack trace.

predicateList

This is a list of any Predicate class objects found in the stack trace.

actionClassList

This is a list of Action classes for any Predicate class objects found in the stack trace.

hasDiagnosticAction()

This method returns true if there is a diagnostic action in the stack trace; otherwise it returns nil.

Modifications to T3StackInfo

The StackTraceInfo class makes use of the following additional methods to the T3StackInfo class:

hasCommand()

This method returns true if the T3StackInfo object has a CommandPhrase class object; otherwise it returns nil.

hasPredicate()

This method returns true if the T3StackInfo object has a Predicate class object, otherwise it returns nil.

getActionClass()

If the T3StackInfo object has a Predicate class object, then this method will return the first named ancestor that represents the Action class for the command.

This file is part of the TADS 3 Proteus Library Extension