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With prototype-based languages, concretization and abstraction are unified into a single concept a prototype. Prototype-based languages are based on a simple set of principles: object-centered representation, dynamic reshape of objects, cloning and possibly message delegation. However, they all differ in the interpretation and combination of these principles. Therefore there is a need to compare and understand. In this paper we present Prototalk, a research and teaching vehicle to understand, implement and compare prototype-based languages. Prototalk is a framework that offers a predefined set of language data structures and mechanisms that can be composed and extended to generate various prototype-based language interpreters. It presents a classification of languages based on different mechanisms in an operational manner.
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Prototalk: an Environment for Teaching, Understanding, Designing
and Prototyping OO Languages Alexandre Bergel, Christophe Dony, Stéphane Ducasse
University of Bern (Switzerland)LIRMM, Montpellier (France)
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Outline
1. Prototype OO Languages
2. Expressing Different Languages
3. Prototalk
4. Example: Newtonscript
5. Conclusion
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Prototype OO Languages
• Classless paradigm
• A prototype contains its state and behavior
• Link between prototypes is usually done using:
• Delegation
• Composition
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Different Languages
• Self: Unification of variables and methods and multiple parents
• ObjectLisp: variables distinct from methods
• NewtonScript: two kinds of delegation over two links
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Prototalk
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Goal and Design Decisions
• Uniformity: same syntax for all the languages
• Minimality: minimal kernel to express the most general semantics
• Extensibility: new languages has to be implemented efficiently and easily
• Usability: integrated in the environment
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Prototalk
• Language represented by a subclass of AbstractProto
• Execution of program by sending evaluate: to it
• The AST is built using a ProgramNodeBuilder
• It is composed of subclass of the Smalltalk AST nodes
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Architecture
AbstractObjectModel
evaluate: sourceCodecompileMethodAt: namecompile: codeSourceglobalVar: varName put: aValuenodeBuilder
NodeBuilder
newVariableName: namenewMessageReceiver: rcvr...
ProgramNode
eval: context
MethodNodeselectorblockeval: contextapplyWith: args in: context
VariableNodevariableNameeval: context
MessageNodeselectoreval: context
Language1variablesmethodsmethodOwner: nameclone...
Language1NodeBuilder
newVariableName: namenewMessageReceiver:...
Language1VariableNode
eval: context
Language1MessageNode
eval: context
Prototalk Base
Implementation of Language1
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Language1
• Language1 is a subclass of AbstractProto
• Ability to execute programs
• Prototypes are represented by its instances
• Provides primitives like clone, addVar: addMethod:, hasVar:, ...
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Example: NewtonScript
• It has a double inheritance: _proto is searched prior to _parent
_parent
_proto
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Double Inheritance
f := {getX: funct() x, _proto: {_proto: {x: 10}}};f._parent := {x: 20};
f getX x: 10
x: 20
_parent
_protof.getX() ==> 10
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In Prototalk
f := {getX: funct() x, _proto: {_proto: {x: 10}}};f._parent := {x: 20};f.getX() ==> 10
The same program in Prototalk:NewtonScriptLike evaluate: ‘ f := PRoot clone. f proto: (PRoot clone; proto: (PRoot clone; addSlot: ‘‘x = 10’’)). f addSlot: ‘‘getX x’’. f parent: (PRoot clone; addSlot: ‘x = 20’). f getX.’
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In PrototalkAbstractProto
NewtonScriptLike parentproto
methodOwner: namemethodOwnerInProto: name
t := self methodOwnerInProto: name.^ t isNil ifTrue: [ parent isNil ifTrue: [nil] ifFalse: [parent methodOwner: name]] ifFalse: [t]]
^ (slots includesKey: name) ifTrue: [self] ifFalse: [ proto isNil ifTrue: [nil] ifFalse: [proto methodOwnerInProto: name]]
slots
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Conclusion
• Platform to design and experiment prototypes-based OO language
• Pure interpretation of programs
• Pedagogical tool: used at University Paris VI, Montpellier and Berne
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• Prototalk: an Environment for Teaching, Understanding, Designing and Prototyping OO languages
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Hierarchy of Object ModelAbstractProto
newEmpty
SlotProtoslotscloneaddSlot: namemethod: codemethodNamed: name
L11
initInitials: slotsnewInitials: slots
L11AndImplicitDelegationparentclonemethodLookup: nameparentson
L16
ModifiableSlot
L7
L7AndImplicitDelegationparentinitializeParent: parentclose
SelfLike
addSlot: slotassignmentMethod: code
L7AndExplicitDelegation
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ProgramNodeBuilder
SelfLikeAssignmentMethodBuilder
Smalltalk ProgramNodeBuilder
Prototalk ProgramNodeBuilder
ProgramNodeBuilder
newCondition(cond, then, else)newLiteralValue(literal)newMessageReceiver(object)newMethodSelector(methName)newVariable(varName)newAssignmentVariable(name)
ImplicitDelegationPNB
newMessageReceiver: object
ImplicitDelegationEncapsulationPNB
newMessageReceiver: objectnewAssignmentVariable: name
ObjectLispLikePNB
newMessageReceiver: object
SelfLikePNB
newVariable: varName
EncapsulationPNB
newVariable: varNamenewAssignmentVariable: name
ExplicitDelegationPNB
newMessageReceiver: object
ExplicitDelegationEncapsulationPNB
newVariable: varNamenewAssignmentVariable: name
AbstractProto
nodeBuilder
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Self, ObjectLisp, ...
Personage=26
name=Luceat=...
Studentnum=1234567
grade=2doExam=...
Personage=26
name=Luceat(...)
Studentnum=1234567
grade=2doExam(...)
