This is the main class used to implement the exception handling system (EHS). It plays two distinct roles: that of the exception, and that of the exception handler. More specifically, it implements the bulk of the protocols laid out in the ANSI specification - those protocol names are reflected in the message categories.

Exception is an abstract class. Instances should neither be created nor trapped. In most cases, subclasses should inherit from Error or Notification rather than directly from Exception.

In implementing this EHS, The Fourth Estate Inc. incorporated some ideas and code from Craig Latta's EHS. His insights were crucial in allowing us to implement BlockContext>>valueUninterruptably (and by extension, #ensure: and #ifCurtailed:), and we imported the following methods with little or no modification:

ContextPart>>terminateTo:
ContextPart>>terminate
MethodContext>>receiver:
MethodContext>>answer:

Thanks, Craig!

	exceptionBuilder
	messageText: tag:

	exceptionDescription
	defaultAction description isResumable messageText tag

	exceptionSignaler
	signal signal:

	private
	findHandlerFrom: handlerAction initialContext: receiver setHandlerFrom:

	signaledException
	isNested outer pass resignalAs: resume resume: retry retryUsing: return return:

	exceptionInstantiator
	signal signal:

	exceptionSelector
	, handles:

	Camp Smalltalk	top
	sunitExitWith:

	exceptionBuilder	top
	messageText: Set an exception's message text.
	tag: This message is not specified in the ANSI protocol, but that looks like an oversight because #tag is specified, and the spec states that the signaler may store the tag value.

	exceptionDescription	top
	defaultAction The default action taken if the exception is signaled.
	description Return a textual description of the exception.
	isResumable Determine whether an exception is resumable.
	messageText Return an exception's message text.
	tag Return an exception's tag value.

	exceptionSignaler	top
	signal Signal the occurrence of an exceptional condition.
	signal: Signal the occurrence of an exceptional condition with a specified textual description.

	private	top
	findHandlerFrom:
	handlerAction
	initialContext:
	receiver
	setHandlerFrom:

	signaledException	top
	isNested Determine whether the current exception handler is within the scope of another handler for the same exception.
	outer Evaluate the enclosing exception action for the receiver and return.
	pass Yield control to the enclosing exception action for the receiver.
	resignalAs: Signal an alternative exception in place of the receiver.
	resume Return from the message that signaled the receiver.
	resume: Return the argument as the value of the message that signaled the receiver.
	retry Abort an exception handler and re-evaluate its protected block.
	retryUsing: Abort an exception handler and evaluate a new block in place of the handler's protected block.
	return Return nil as the value of the block protected by the active exception handler.
	return: Return the argument as the value of the block protected by the active exception handler.

	Camp Smalltalk	top
	sunitSignalWith:

	exceptionInstantiator	top
	signal Signal the occurrence of an exceptional condition.
	signal: Signal the occurrence of an exceptional condition with a specified textual description.

	exceptionSelector	top
	, Create an exception set.
	handles: Determine whether an exception handler will accept a signaled exception.