I represent the machine state at the time of an interrupted process. I also represent a query path into the state of the process. The debugger is typically viewed through a window that views the stack of suspended contexts, the code for, and execution point in, the currently selected message, and inspectors on both the receiver of the currently selected message, and the variables in the current context.

Special note on recursive errors:
Some errors affect Squeak's ability to present a debugger. This is normally an unrecoverable situation. However, if such an error occurs in an isolation layer, Squeak will attempt to exit from the isolation layer and then present a debugger. Here is the chain of events in such a recovery.

* A recursive error is detected.
* The current project is queried for an isolationHead
* Changes in the isolationHead are revoked
* The parent project of isolated project is returned to
* The debugger is opened there and execution resumes.

If the user closes that debugger, execution continues in the outer project and layer. If, after repairing some damage, the user proceeds from the debugger, then the isolationHead is re-invoked, the failed project is re-entered, and execution resumes in that world.

	class list
	selectedClass selectedClassOrMetaClass

	code pane
	contentsSelection createSyntaxMorph doItContext doItReceiver pc pcRange toggleSyntaxMorph

	code pane menu
	perform:orSendTo:

	context stack (message list)
	contextStackIndex contextStackList expandStack fullyExpandStack messageListIndex selectedMessage selectedMessageName toggleContextStackIndex:

	context stack menu
	abandon abandon: browseMessages browseSendersOfMessages browseVersions buildMessageBrowser buildMorphicNotifierLabelled:message: close: contextStackKey:from: contextStackMenu:shifted: currentCompiledMethod debugProceedMenu: doStep down fullStack mailOutBugReport messageListMenu:shifted: peelToFirst proceed proceed: restart selectPC send stepIntoBlock up where

	dependents access
	step updateInspectors wantsSteps

initialize

buildMVCDebuggerViewLabel:minSize: buildMVCNotifierButtonView buildMVCNotifierViewLabel:message:minSize: buildMVCOptionalButtonsButtonsView buttonRowForPreDebugWindow: debugAt: notifierButtonHeight openFullMorphicLabel: openFullNoSuspendLabel: openNotifierContents:label: optionalAnnotationHeight optionalButtonHeight optionalButtonPairs optionalButtonRow preDebugButtonQuads preDebugNotifierContentsFrom: release wantsOptionalButtons windowIsClosing

	message category list
	selectedMessageCategoryName

	notifier menu
	debug

	private
	checkContextSelection contextStackIndex:oldContextWas: externalInterrupt: isolationRecoveryAdvice lowSpaceChoices newStack: process:controller:context: process:controller:context:isolationHead: resetContext: resumeProcess: selectedContext

	instance creation
	context: context:isolationHead: informExistingDebugger:label:

	opening
	openInterrupt:onProcess:

	accessing	top
	contents Depending on the current selection, different information is retrieved. Answer a string description of that information. This information is the method in the currently selected context.
	contents:notifying: The retrieved information has changed and its source must now be updated. In this case, the retrieved information is the method of the selected context.
	contextVariablesInspector Answer the instance of Inspector that is providing a view of the variables of the selected context.
	doNothing: Notifier window can't accept text
	interruptedContext Answer the suspended context of the interrupted process.
	interruptedProcess Answer the interrupted process.
	isNotifier Return true if this debugger has not been expanded into a full sized window
	labelString
	labelString:
	proceedValue Answer the value to return to the selected context when the interrupted process proceeds.
	proceedValue: Set the value to be returned to the selected context when the interrupted process proceeds.
	receiver Answer the receiver of the selected context, if any. Answer nil otherwise.
	receiverInspector Answer the instance of Inspector that is providing a view of the variables of the selected context's receiver.

	class list	top
	selectedClass Answer the class in which the currently selected context's method was found.
	selectedClassOrMetaClass Answer the class in which the currently selected context's method was found.

	code pane	top
	contentsSelection Return the interval of text in the code pane to select when I set the pane's contents
	createSyntaxMorph
	doItContext Answer the context in which a text selection can be evaluated.
	doItReceiver Answer the object that should be informed of the result of evaluating a text selection.
	pc
	pcRange Answer the indices in the source code for the method corresponding to the selected context's program counter value.
	toggleSyntaxMorph syntaxMorph ifNil: [syntaxMorph _ self createSyntaxMorph inAScrollPane. syntaxMorph color: Color paleOrange]. standardTextMorph visible ifTrue: [ standardTextMorph owner replacePane: standardTextMorph with: syntaxMorph. syntaxMorph scroller firstSubmorph update: #contentsSelection. ] ifFalse: [ syntaxMorph owner replacePane: syntaxMorph with: standardTextMorph. ].

	code pane menu	top
	perform:orSendTo: Selector was just chosen from a menu by a user. If can respond, then perform it on myself. If not, send it to otherTarget, presumably the editPane from which the menu was invoked.

	context stack (message list)	top
	contextStackIndex Answer the index of the selected context.
	contextStackList Answer the array of contexts.
	expandStack A Notifier is being turned into a full debugger. Show a substantial amount of stack in the context pane.
	fullyExpandStack Expand the stack to include all of it, rather than the first four or five contexts.
	messageListIndex Answer the index of the currently selected context.
	selectedMessage Answer the source code of the currently selected context.
	selectedMessageName Answer the message selector of the currently selected context.
	toggleContextStackIndex: If anInteger is the same as the index of the selected context, deselect it. Otherwise, the context whose index is anInteger becomes the selected context.

	context stack menu	top
	abandon abandon the debugger from its pre-debug notifier
	abandon: abandon the notifier represented by aTopView
	browseMessages Present a menu of all messages sent by the currently selected message. Open a message set browser of all implementors of the message chosen. Do nothing if no message is chosen.
	browseSendersOfMessages Present a menu of the currently selected message, as well as all messages sent by it. Open a message set browser of all implementors of the message chosen.
	browseVersions Create and schedule a message set browser on all versions of the currently selected message selector.
	buildMessageBrowser Create and schedule a message browser on the current method.
	buildMorphicNotifierLabelled:message:
	close: The argument is a controller on a view of the receiver. That view is closed.
	contextStackKey:from: Respond to a keystroke in the context list
	contextStackMenu:shifted: Set up the menu appropriately for the context-stack-list, either shifted or unshifted as per the parameter provided
	currentCompiledMethod
	debugProceedMenu:
	doStep Send the selected message in the accessed method, and regain control after the invoked method returns.
	down move down the context stack to the previous (enclosing) context
	fullStack Change from displaying the minimal stack to a full one.
	mailOutBugReport Compose a useful bug report showing the state of the process as well as vital image statistics as suggested by Chris Norton - 'Squeak could pre-fill the bug form with lots of vital, but oft-repeated, information like what is the image version, last update number, VM version, platform, available RAM, author...' and address it to the list with the appropriate subject prefix.
	messageListMenu:shifted: The context-stack menu takes the place of the message-list menu in the debugger, so pass it on
	peelToFirst Peel the stack back to the second occurance of the currently selected message. Very useful for an infinite recursion. Gets back to the second call so you can see one complete recursion cycle, and how it was called at the beginning. Also frees a lot of space!
	proceed Proceed execution of the receiver's model, starting after the expression at which an interruption occurred.
	proceed: Proceed from the interrupted state of the currently selected context. The argument is the topView of the receiver. That view is closed.
	restart Proceed from the initial state of the currently selected context. The argument is a controller on a view of the receiver. That view is closed.
	selectPC Toggle the flag telling whether to automatically select the expression currently being executed by the selected context.
	send Send the selected message in the accessed method, and take control in the method invoked to allow further step or send.
	stepIntoBlock Send messages until you return to the present method context. Used to step into a block in the method.
	up move up the context stack to the next (enclosed) context
	where Select the expression whose evaluation was interrupted.

	dependents access	top
	step Update the inspectors.
	updateInspectors Update the inspectors on the receiver's variables.
	wantsSteps Overridden by morphic classes whose instances want to be stepped, or by model classes who want their morphic views to be stepped.

	initialize	top
	buildMVCDebuggerViewLabel:minSize: Build an MVC debugger view around the receiver, and return the StandardSystemView thus created.
	buildMVCNotifierButtonView
	buildMVCNotifierViewLabel:message:minSize:
	buildMVCOptionalButtonsButtonsView
	buttonRowForPreDebugWindow:
	debugAt:
	notifierButtonHeight
	openFullMorphicLabel: Open a full morphic debugger with the given label
	openFullNoSuspendLabel: Create and schedule a full debugger with the given label. Do not terminate the current active process.
	openNotifierContents:label: Create and schedule a notifier view with the given label and message. A notifier view shows just the message or the first several lines of the stack, with a menu that allows the user to open a full debugger if so desired.
	optionalAnnotationHeight
	optionalButtonHeight
	optionalButtonPairs Actually, return triples
	optionalButtonRow Answer a button pane affording the user one-touch access to certain functions; the pane is given the formal name 'buttonPane' by which it can be retrieved by code wishing to send messages to widgets residing on the pane
	preDebugButtonQuads
	preDebugNotifierContentsFrom:
	release Remove references to objects that may refer to the receiver. This message should be overridden by subclasses with any cycles, in which case the subclass should also include the expression super release.
	wantsOptionalButtons The debugger benefits so majorly from the optional buttons that we put them up regardless of the global setting. Some traditionalists will want to change this method manually!
	windowIsClosing My window is being closed; clean up. Restart the low space watcher.

	message category list	top
	selectedMessageCategoryName Answer the name of the message category of the message of the currently selected context.

	notifier menu	top
	debug Open a full DebuggerView.

	private	top
	checkContextSelection
	contextStackIndex:oldContextWas:
	externalInterrupt:
	isolationRecoveryAdvice Return a notifier message string to be presented in case of recovery from recursive error by revoking the changes in an isolation layer. This surely ranks as one of Squeak's longer help messages.
	lowSpaceChoices Return a notifier message string to be presented when space is running low.
	newStack:
	process:controller:context:
	process:controller:context:isolationHead:
	resetContext: Used when a new context becomes top-of-stack, for instance when the method of the selected context is re-compiled, or the simulator steps or returns to a new method. There is room for much optimization here, first to save recomputing the whole stack list (and text), and secondly to avoid recomposing all that text (by editing the paragraph instead of recreating it).
	resumeProcess:
	selectedContext

	class initialization	top
	initialize The class variables were initialized once, and subsequently filled with information. Re-executing this method is therefore dangerous.
	openContext:label:contents: Open a notifier in response to an error, halt, or notify. A notifier view just shows a short view of the sender stack and provides a menu that lets the user open a full debugger.

	instance creation	top
	context: Answer an instance of me for debugging the active process starting with the given context.
	context:isolationHead: Answer an instance of me for debugging the active process starting with the given context.
	informExistingDebugger:label: Walking the context chain, we try to find out if we're in a debugger stepping situation. If we find the relevant contexts, we must rearrange them so they look just like they would if the methods were excuted outside of the debugger.

	opening	top
	openInterrupt:onProcess: Open a notifier in response to an interrupt. An interrupt occurs when the user types the interrupt key (cmd-. on Macs, ctrl-c or alt-. on other systems) or when the low-space watcher detects that memory is low.