amber/st/Compiler-Interpreter.st

Smalltalk current createPackage: 'Compiler-Interpreter'!
NodeVisitor subclass: #AIContext
	instanceVariableNames: 'outerContext innerContext pc locals method ast interpreter methodContext'
	package: 'Compiler-Interpreter'!
!AIContext commentStamp!
I am like a `MethodContext`, used by the `ASTInterpreter`.
Unlike a `MethodContext`, my instances are not read-only.

When debugging, my instances are created by copying the current `MethodContext` (thisContext)!

!AIContext methodsFor: 'accessing'!

home
	^ self isBlockContext 
		ifTrue: [ self outerContext methodContext ]
		ifFalse: [ self ]
!

innerContext
	^ innerContext
!

innerContext: anAIContext
	innerContext := anAIContext
!

localAt: aString
	^ self locals at: aString ifAbsent: [ nil ]
!

localAt: aString put: anObject
	self locals at: aString put: anObject
!

locals
	locals ifNil: [ self initializeLocals ].
	
	^ locals
!

method
	^ method
!

method: aCompiledMethod
	method := aCompiledMethod
!

outerContext
	^ outerContext
!

outerContext: anAIContext
	outerContext := anAIContext.
	outerContext innerContext: self
!

selector
	^ self method ifNotNil: [ 
		self method selector ]
! !

!AIContext methodsFor: 'converting'!

asString
	^ methodContext asString
! !

!AIContext methodsFor: 'initialization'!

initializeAST
	ast := self method ast.
	(SemanticAnalyzer on: self method methodClass)
		visit: ast
!

initializeFromMethodContext: aMethodContext
	methodContext := aMethodContext.
	
	self pc: aMethodContext pc.
	self receiver: aMethodContext receiver.
	self method: aMethodContext method.
	aMethodContext outerContext ifNotNil: [ :outer |
		"If the method context is nil, the block was defined in JS, so ignore it"
		outer methodContext ifNotNil: [
			self outerContext: (self class fromMethodContext: aMethodContext outerContext) ].
			aMethodContext locals keysAndValuesDo: [ :key :value |
				self locals at: key put: value ] ]
!

initializeInterpreter
	interpreter := Interpreter new
		context: self;
		node: self retrieveNode;
		yourself.
	self innerContext isBlockContext ifFalse: [
		self setupInterpreter: interpreter ]
!

initializeLocals
	locals := Dictionary new.
	locals at: 'thisContext' put: self.
! !

!AIContext methodsFor: 'interpreting'!

arguments
	^ self ast arguments collect: [ :each |
		self localAt: each ]
!

ast
	ast ifNil: [ self initializeAST ].
	^ ast
!

interpreter
	interpreter ifNil: [ self initializeInterpreter ].
	^ interpreter
!

pc
	^ pc ifNil: [ pc := 0 ]
!

pc: anInteger
	pc := anInteger
!

receiver
	^ self localAt: 'self'
!

receiver: anObject
	self localAt: 'self' put: anObject
!

retrieveNode
	^ ASTPCNodeVisitor new
		context: self;
		visit: self ast;
		currentNode
!

setupInterpreter: anInterpreter
	"Push the send args and receiver to the interpreter stack"
	
	self innerContext arguments reversed do: [ :each | 
		anInterpreter push: each ].
		
	anInterpreter push: (self innerContext receiver)
! !

!AIContext methodsFor: 'testing'!

isBlockContext
	^ methodContext isBlockContext
! !

!AIContext class methodsFor: 'instance creation'!

fromMethodContext: aMethodContext
	^ self new
		initializeFromMethodContext: aMethodContext;
		yourself
! !

Object subclass: #ASTDebugger
	instanceVariableNames: 'interpreter context'
	package: 'Compiler-Interpreter'!
!ASTDebugger commentStamp!
I am a stepping debugger interface for Amber code.
I internally use an instance of `ASTSteppingInterpreter` to actually step through node and interpret them.

My instances are created from a `MethodContext` with `ASTDebugger class >> context:`.
They hold an `AIContext` instance internally, recursive copy of the `MethodContext`.

## API

Use the methods of the `'stepping'` protocol to do stepping.!

!ASTDebugger methodsFor: 'accessing'!

context
	^ context
!

context: aContext
	context := aContext
!

interpreter
	^ interpreter ifNil: [ interpreter := self defaultInterpreterClass new ]
!

interpreter: anInterpreter
	interpreter := anInterpreter
!

method
	^ self context method
!

nextNode
	^ self interpreter nextNode
! !

!ASTDebugger methodsFor: 'defaults'!

defaultInterpreterClass
	^ ASTSteppingInterpreter
! !

!ASTDebugger methodsFor: 'initialization'!

buildAST
	"Build the AST tree from the method source code.
	The AST is annotated with a SemanticAnalyzer,
	to know the semantics and bindings of each node needed for later debugging"
	
	| ast |
	
	ast := Smalltalk current parse: self method source.
	(SemanticAnalyzer on: self context receiver class)
		visit: ast.
	
	^ ast
!

initializeInterpreter
	| ast next |
	ast := self buildAST.
	next := ASTPCNodeVisitor new
		context: self context;
		visit: ast;
		currentNode.
	self interpreter interpret: next
!

initializeWithContext: aContext
	"TODO: do we need to handle block contexts?"
	
	self context: aContext.
	self initializeInterpreter
! !

!ASTDebugger methodsFor: 'stepping'!

proceed
	self shouldBeImplemented
!

restart
	self shouldBeImplemented
!

step
	"The ASTSteppingInterpreter stops at each node interpretation.
	One step will interpret nodes until:
	- we get at the end
	- the next node is a stepping node (send, assignment, etc.)"
	
	[ (self interpreter nextNode notNil and: [ self interpreter nextNode stopOnStepping ])
		or: [ self interpreter atEnd not ] ]
			whileFalse: [
				self interpreter step.
				self step ]
!

stepInto
	self shouldBeImplemented
!

stepOver
	self step
! !

!ASTDebugger methodsFor: 'testing'!

atEnd
	^ self interpreter atEnd
! !

!ASTDebugger class methodsFor: 'instance creation'!

context: aContext
	^ self new
		initializeWithContext: aContext;
		yourself
! !

Object subclass: #ASTInterpreter
	instanceVariableNames: 'currentNode nextNode context shouldReturn result'
	package: 'Compiler-Interpreter'!
!ASTInterpreter commentStamp!
I am like a `NodeVisitor`, interpreting nodes one after each other.
I am built using Continuation Passing Style for stepping purposes.

## Usage example:

	| ast interpreter |
	ast := Smalltalk current parse: 'foo 1+2+4'.
	(SemanticAnalyzer on: Object) visit: ast.

	ASTInterpreter new
		interpret: ast nodes first;
		result "Answers 7"!

!ASTInterpreter methodsFor: 'accessing'!

context
	^ context ifNil: [ context := AIContext new ]
!

context: anAIContext
	context := anAIContext
!

currentNode
	^ currentNode
!

nextNode
	^ nextNode ifNil: [ self currentNode ]
!

nextNode: aNode
	nextNode := aNode
!

result
	^ result
! !

!ASTInterpreter methodsFor: 'initialization'!

initialize
	super initialize.
	shouldReturn := false
! !

!ASTInterpreter methodsFor: 'interpreting'!

interpret: aNode
	shouldReturn := false.
	self interpret: aNode continue: [ :value |
		result := value ]
!

interpret: aNode continue: aBlock
	shouldReturn ifTrue: [ ^ self ].

	aNode isNode
		ifTrue: [
			currentNode := aNode.
			self interpretNode: aNode continue: [ :value |
				self continue: aBlock value: value ] ]
		ifFalse: [ self continue: aBlock value: aNode ]
!

interpretAssignmentNode: aNode continue: aBlock
	self interpret: aNode right continue: [ :value |
		self
			continue: aBlock
			value: (self assign: aNode left to: value) ]
!

interpretBlockNode: aNode continue: aBlock
	self
		continue: aBlock
		value: [ 
			self withBlockContext: [ 
				self interpret: aNode nodes first; result ] ]
!

interpretBlockSequenceNode: aNode continue: aBlock
	self interpretSequenceNode: aNode continue: aBlock
!

interpretCascadeNode: aNode continue: aBlock
	"TODO: Handle super sends"
	
	self interpret: aNode receiver continue: [ :receiver |
		"Only interpret the receiver once"
		aNode nodes do: [ :each | each receiver: receiver ].

		self
			interpretAll: aNode nodes allButLast
			continue: [
				self
					interpret: aNode nodes last
					continue: [ :val | self continue: aBlock value: val ] ] ]
!

interpretClassReferenceNode: aNode continue: aBlock
	self continue: aBlock value: (Smalltalk current at: aNode value)
!

interpretDynamicArrayNode: aNode continue: aBlock
	self interpretAll: aNode nodes continue: [ :array |
		self
			continue: aBlock
			value: array ]
!

interpretDynamicDictionaryNode: aNode continue: aBlock
	self interpretAll: aNode nodes continue: [ :array | | hashedCollection |
		hashedCollection := HashedCollection new.
		array do: [ :each | hashedCollection add: each ].
		self
			continue: aBlock
			value: hashedCollection ]
!

interpretJSStatementNode: aNode continue: aBlock
	shouldReturn := true.
	self continue: aBlock value: (self eval: aNode source)
!

interpretMethodNode: aNode continue: aBlock
	self interpretAll: aNode nodes continue: [ :array |
		self continue: aBlock value: array first ]
!

interpretNode: aNode continue: aBlock
	aNode interpreter: self continue: aBlock
!

interpretReturnNode: aNode continue: aBlock
	self interpret: aNode nodes first continue: [ :value |
		shouldReturn := true.
		self continue: aBlock value: value ]
!

interpretSendNode: aNode continue: aBlock
	self interpret: aNode receiver continue: [ :receiver |
		self interpretAll: aNode arguments continue: [ :args |
			self
				messageFromSendNode: aNode
				arguments: args
				do: [ :message |
					self context pc: self context pc + 1.
					self
						continue: aBlock
						value: (self sendMessage: message to: receiver superSend: aNode superSend) ] ] ]
!

interpretSequenceNode: aNode continue: aBlock
	self interpretAll: aNode nodes continue: [ :array |
		self continue: aBlock value: array last ]
!

interpretValueNode: aNode continue: aBlock
	self continue: aBlock value: aNode value
!

interpretVariableNode: aNode continue: aBlock
	self
		continue: aBlock
		value: (aNode binding isInstanceVar
			ifTrue: [ self context receiver instVarAt: aNode value ]
			ifFalse: [ self context localAt: aNode value ])
! !

!ASTInterpreter methodsFor: 'private'!

assign: aNode to: anObject
	^ aNode binding isInstanceVar
		ifTrue: [ self context receiver instVarAt: aNode value put: anObject ]
		ifFalse: [ self context localAt: aNode value put: anObject ]
!

continue: aBlock value: anObject
	result := anObject.
	aBlock value: anObject
!

eval: aString
	"Evaluate aString as JS source inside an JS function.
	aString is not sandboxed."
	
	| source function |
	
	source := String streamContents: [ :str |
		str nextPutAll: '(function('.
		self context locals keys
			do: [ :each | str nextPutAll: each ]
			separatedBy: [ str nextPutAll: ',' ].
		str
			nextPutAll: '){ return (function() {';
			nextPutAll: aString;
			nextPutAll: '})() })' ].
			
	function := Compiler new eval: source.
	
	^ function valueWithPossibleArguments: self context locals values
!

interpretAll: aCollection continue: aBlock
	self
		interpretAll: aCollection
		continue: aBlock
		result: OrderedCollection new
!

interpretAll: nodes continue: aBlock result: aCollection
	nodes isEmpty
		ifTrue: [ self continue: aBlock value: aCollection ]
		ifFalse: [
			self interpret: nodes first continue: [:value |
				self
					interpretAll: nodes allButFirst
					continue: aBlock
					result: aCollection, { value } ] ]
!

messageFromSendNode: aSendNode arguments: aCollection do: aBlock
	self
		continue: aBlock
		value: (Message new
			selector: aSendNode selector;
			arguments: aCollection;
			yourself)
!

sendMessage: aMessage to: anObject superSend: aBoolean
	| method |
	
	aBoolean ifFalse: [ ^ aMessage sendTo: anObject ].
	anObject class superclass ifNil: [ ^ self messageNotUnderstood: aMessage receiver: anObject ].
	
	method := anObject class superclass methodDictionary
		at: aMessage selector
		ifAbsent: [ ^ self messageNotUnderstood: aMessage receiver: anObject ].
		
	^ method fn applyTo: anObject arguments: aMessage arguments
!

withBlockContext: aBlock
	"Evaluate aBlock with a BlockContext:
	- a context is pushed before aBlock evaluation.
	- the context is poped after aBlock evaluation
	- the result of aBlock evaluation is answered"
	
	| blockResult |
			
	self context: (AIContext new
		outerContext: self context;
		yourself).
	
	blockResult := aBlock value.
	
	self context: self context outerContext.
	^ blockResult
! !

!ASTInterpreter methodsFor: 'testing'!

shouldReturn
	^ shouldReturn ifNil: [ false ]
! !

ASTInterpreter subclass: #ASTSteppingInterpreter
	instanceVariableNames: 'continuation nextNode'
	package: 'Compiler-Interpreter'!
!ASTSteppingInterpreter commentStamp!
I am an interpreter with stepping capabilities. The higher level `ASTDebugger` class should be used as a debugger model, as it provides convenience methods for debugging.

## API

Use `#step` to actually interpret the next node. Interpretation stops at each node evaluation, weither it's a message node or not.


## Usage example:

	| ast interpreter |
	ast := Smalltalk current parse: 'foo 1+2+4'.
	(SemanticAnalyzer on: Object) visit: ast.

	interpreter := ASTSteppingInterpreter new
		interpret: ast nodes first;
		yourself.
		
	interpreter step; step.
	interpreter step; step.
	interpreter result."Answers 1"
	interpreter step.
	interpreter result. "Answers 3"
	interpreter step.
	interpreter result. "Answers 7"!

!ASTSteppingInterpreter methodsFor: 'accessing'!

nextNode
	^ nextNode
! !

!ASTSteppingInterpreter methodsFor: 'initialization'!

initialize
	super initialize.
	continuation := []
! !

!ASTSteppingInterpreter methodsFor: 'interpreting'!

interpret: aNode continue: aBlock
	nextNode := aNode.
	continuation := [
		super interpret: aNode continue: aBlock ]
! !

!ASTSteppingInterpreter methodsFor: 'stepping'!

step
	continuation value
! !

!ASTSteppingInterpreter methodsFor: 'testing'!

atEnd
	^ self shouldReturn or: [ self nextNode == self currentNode ]
! !

NodeVisitor subclass: #ASTPCNodeVisitor
	instanceVariableNames: 'useInlinings pc context currentNode'
	package: 'Compiler-Interpreter'!
!ASTPCNodeVisitor commentStamp!
I visit an AST until I get to the current pc node and answer it.

## API

My instances must be filled with a context object using `#context:`.

After visiting the AST the current node corresponding to the `pc` is answered by `#currentNode`!

!ASTPCNodeVisitor methodsFor: 'accessing'!

context
	^ context
!

context: aContext
	context := aContext
!

currentNode
	^ currentNode
!

pc
	^ pc ifNil: [ 0 ]
!

pc: anInteger
	pc := anInteger
!

useInlinings
	^ useInlinings ifNil: [ true ]
!

useInlinings: aBoolean
	useInlinings := aBoolean
! !

!ASTPCNodeVisitor methodsFor: 'visiting'!

visitJSStatementNode: aNode
	currentNode := aNode
!

visitSendNode: aNode
	super visitSendNode: aNode.
	
	self pc = self context pc ifFalse: [
		aNode shouldBeInlined ifFalse: [ 
			self pc: self pc + 1.
			currentNode := aNode ] ]
! !

NodeVisitor subclass: #Interpreter
	instanceVariableNames: 'node context stack returnValue'
	package: 'Compiler-Interpreter'!

!Interpreter methodsFor: 'accessing'!

context
	^ context
!

context: aContext
	context := aContext
!

node
	"Answer the next node, ie the node to be evaluated in the next step"
	
	^ node
!

node: aNode
	node := aNode
!

result
	^ self returnValue ifNil: [ self context receiver ]
!

returnValue
	^ returnValue
!

returnValue: anObject
	returnValue := anObject
!

stack
	^ stack ifNil: [ stack := OrderedCollection new ]
! !

!Interpreter methodsFor: 'interpreting'!

interpret
	"Interpret the next node to be evaluated"
	
	self visit: self node
!

interpret: aNode
	self node: aNode.
	self interpret
!

next
	self node: self node nextNode
!

proceed
	"Eagerly evaluate the ast"
	
	[ self atEnd ] whileFalse: [ 
		self step ]
!

restart
	self node: self context ast nextChild
!

skip
	self next
!

step
	self 
		interpret; 
		next
!

stepOver
	self step.
	
	[ self node isSteppingNode ] whileFalse: [ 
		self step ]
! !

!Interpreter methodsFor: 'private'!

assign: aNode to: anObject
	aNode binding isInstanceVar
		ifTrue: [ self context receiver instVarAt: aNode value put: anObject ]
		ifFalse: [ self context localAt: aNode value put: anObject ]
!

eval: aString
	"Evaluate aString as JS source inside an JS function.
	aString is not sandboxed."
	
	| source function |
	
	source := String streamContents: [ :str |
		str nextPutAll: '(function('.
		self context locals keys
			do: [ :each | str nextPutAll: each ]
			separatedBy: [ str nextPutAll: ',' ].
		str
			nextPutAll: '){ return (function() {';
			nextPutAll: aString;
			nextPutAll: '})() })' ].
			
	function := Compiler new eval: source.
	
	^ function valueWithPossibleArguments: self context locals values
!

messageFromSendNode: aSendNode arguments: aCollection
	^ Message new
		selector: aSendNode selector;
		arguments: aCollection;
		yourself
!

messageNotUnderstood: aMessage receiver: anObject
	MessageNotUnderstood new
		meesage: aMessage;
		receiver: anObject;
		signal
!

sendMessage: aMessage to: anObject superSend: aBoolean
	| method |
	
	aBoolean ifFalse: [ ^ aMessage sendTo: anObject ].
	anObject class superclass ifNil: [ ^ self messageNotUnderstood: aMessage receiver: anObject ].
	
	method := anObject class superclass methodDictionary
		at: aMessage selector
		ifAbsent: [ ^ self messageNotUnderstood: aMessage receiver: anObject ].
		
	^ method sendTo: anObject arguments: aMessage arguments
! !

!Interpreter methodsFor: 'stack'!

peek
	"Peek the top object of the context stack"
	
	^ self stack last
!

pop
	"Pop an object from the context stack"
	
	| value |
	
	value := self peek.
	self stack removeLast.
	^ value
!

push: anObject
	"Push an object to the context stack"
	
	^ self stack add: anObject
! !

!Interpreter methodsFor: 'testing'!

atEnd
	^ self shouldReturn or: [ self node isNil ]
!

shouldReturn
	^ self returnValue notNil
! !

!Interpreter methodsFor: 'visiting'!

visit: aNode
	self shouldReturn ifFalse: [ super visit: aNode ]
!

visitAssignmentNode: aNode
	| value |
	
	value := self pop.
	
	"Pop the left side of the assignment.
	It already has been visited, and we don't need its value."
	self pop.
	
	self push: value.
	self assign: aNode left to: value
!

visitBlockNode: aNode
	"Do not evaluate the block node.
	Instead, put all instructions into a block that we push to the stack for later evaluation"
	
	| blockNode blockContext block interpreter |
	
	"Copy the sequence node without the parent to avoid evaluating nodes up the block. 
	#nextNode should not go anymore up than the block itself"
	blockNode := aNode nodes first copy.
	blockNode parent: nil.
		
	blockContext := self context class new
		outerContext: self context;
		yourself.
	
	block := [
		interpreter := self class new.
		interpreter
			context: blockContext;
			node: blockNode nextChild;
			proceed.
		
		"Non local returns hanlding"
		self returnValue: interpreter returnValue.
		
		"Answer the last evaluation of the block or nil"
		interpreter stack isEmpty
			ifTrue: [ nil ]
			ifFalse: [ interpreter pop ] ].
	
	self push: block
!

visitClassReferenceNode: aNode
	self push: (Smalltalk current at: aNode value)
!

visitDynamicArrayNode: aNode
	| array |
	
	array := #().
	aNode nodes do: [ :each |
		array addFirst: self pop ].
	
	self push: array
!

visitDynamicDictionaryNode: aNode
	| hashedCollection |
	
	hashedCollection := HashedCollection new.
	aNode nodes do: [ :each | 
		hashedCollection add: self pop ].
	
	self push: hashedCollection
!

visitJSStatementNode: aNode
	self returnValue: (self eval: aNode source)
!

visitNode: aNode
	"Do nothing by default. Especially, do not visit children recursively."
!

visitReturnNode: aNode
	self returnValue: self pop
!

visitSendNode: aNode
	| receiver args message result |
	
	args := aNode arguments collect: [ :each | self pop ].
	receiver := self pop.
	
	message := self
		messageFromSendNode: aNode
		arguments: args reversed.
	
	result := self sendMessage: message to: receiver superSend: aNode superSend.
	
	self context pc: self context pc + 1.
	
	"For cascade sends, push the reciever if the send is not the last one"
	(aNode isCascadeSendNode and: [ aNode isLastChild not ])
		ifTrue: [ self push: receiver ]
		ifFalse: [ self push: result ]
!

visitValueNode: aNode
	self push: aNode value
!

visitVariableNode: aNode
	"TODO: what about other vars (JS globals for instance)?"
	
	self push: (aNode binding isInstanceVar
		ifTrue: [ self context receiver instVarAt: aNode value ]
		ifFalse: [ self context localAt: aNode value ])
! !

!Node methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretNode: self continue: aBlock
!

isSteppingNode
	^ false
! !

!AssignmentNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretAssignmentNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!BlockNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretBlockNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!CascadeNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretCascadeNode: self continue: aBlock
! !

!DynamicArrayNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretDynamicArrayNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!DynamicDictionaryNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretDynamicDictionaryNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!JSStatementNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretJSStatementNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!MethodNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretMethodNode: self continue: aBlock
! !

!ReturnNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretReturnNode: self continue: aBlock
! !

!SendNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretSendNode: self continue: aBlock
!

isSteppingNode
	^ true
! !

!SequenceNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretSequenceNode: self continue: aBlock
! !

!BlockSequenceNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretBlockSequenceNode: self continue: aBlock
! !

!ValueNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretValueNode: self continue: aBlock
! !

!VariableNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretVariableNode: self continue: aBlock
! !

!ClassReferenceNode methodsFor: '*Compiler-Interpreter'!

interpreter: anInterpreter continue: aBlock
	^ anInterpreter interpretClassReferenceNode: self continue: aBlock
! !