Reflection in Pharo: Beyond Smalltak
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The document discusses advanced features of reflection in Pharo, focusing on the Object-oriented programming paradigm and the manipulation of Abstract Syntax Trees (ASTs). It presents how ASTs can be enhanced with annotations and used to improve the compiler, along with examples demonstrating the integration of reflective methods and concepts like metalinks. The talk also addresses the idea of refining variable handling and improving the API for globals and class variables, envisioning a future where bindings and slots are treated as first-class objects.
![DEMO
(OrderedCollection>>#do:) ast.
[ 1 + 2 ] sourceNode == thisContext method ast blockNodes first
• ASTCache: as twice, get the same answer
(flushed on image save for now)](https://image.slidesharecdn.com/2016-brussels-160901092957/85/Reflection-in-Pharo-Beyond-Smalltak-11-320.jpg)
![Link: metaobject
The object to send
a message to
link := MetaLink new
metaObject: [self halt]](https://image.slidesharecdn.com/2016-brussels-160901092957/85/Reflection-in-Pharo-Beyond-Smalltak-30-320.jpg)
![Link: condition
boolean or block
link := MetaLink new
…..
condition: [self someCheck]](https://image.slidesharecdn.com/2016-brussels-160901092957/85/Reflection-in-Pharo-Beyond-Smalltak-35-320.jpg)
![Reifications: condition
link := MetaLink new
condition: [: object | object == 1];](https://image.slidesharecdn.com/2016-brussels-160901092957/85/Reflection-in-Pharo-Beyond-Smalltak-39-320.jpg)
![Statement Coverage
link := MetaLink new
metaObject: #node;
selector: #tagExecuted.
“set this link on all the AST nodes"
(ReflectivityExamples>>#exampleMethod) ast
nodesDo: [:node | node link: link].](https://image.slidesharecdn.com/2016-brussels-160901092957/85/Reflection-in-Pharo-Beyond-Smalltak-41-320.jpg)
Reflection in Pharo: Beyond Smalltak
- 1. Reflection in Pharo: Beyond Smalltak Marcus Denker http://www.pharo.org Talk held at SOFT, VUB, Brussels Jan 2016
- 2. Everything is an Object
- 3. Classes
- 4. Methods
- 5. The Stack
- 6. Everything is an Object
- 7. Code?
- 8. AST: Abstract Syntax Tree
- 9. AST in Pharo5 • AST of the Refactoring browser • Transformation • Visitors • Annotations (properties) • Deeper integrated: • Pretty Printing, Syntax Highlight, Suggestions • Compiler uses RB AST
- 10. AST in Pharo5 • Easy access • #ast • Demo: method and block
- 11. DEMO (OrderedCollection>>#do:) ast. [ 1 + 2 ] sourceNode == thisContext method ast blockNodes first • ASTCache: as twice, get the same answer (flushed on image save for now)
- 12. AST + Tools
- 13. Opal Compiler • Uses RB AST • Based on Visitors Text AST AST +vars IR CM Parser Semantic Analysis AST Translator+ IRBuilder BytecodeBuilder+ Encoder
- 14. Opal: API • All staged are Pluggable • e.g Semantic Analyzer or Code Generator can be changed. • compiler options
- 15. Opal: Bytecode editing • IR can be used to manipulate methods on a bytecode level Text AST AST +vars IR CM Parser Semantic Analysis AST Translator+ IRBuilder BytecodeBuilder+ Encoder
- 16. Too complicated
- 17. Too low level
- 18. Can we do better?
- 19. AST Meta Annotation • We have an AST with properties • We have Opal with Pluggable API
- 20. Can’t we use that?
- 21. Basis: the Evil Twin CompiledMethod ReflectiveMethod Know each other Bytecode AST
- 22. Basis: the Evil Twin ReflectiveMethod AST run: aSelector with: anArray in: aReceiver self installCompiledMethod. self recompileAST. self installCompiledMethod. ^compiledMethod valueWithReceiver: aReceiver arguments: anArray
- 23. Demo: Morph • Morph methods do: #createTwin • Morph methods do: #invalidate • inspect “Morph methods”
- 24. Putting it together • Annotate the AST • Create Twin if needed • Invalidate method • Next call: generate code changed by annotation
- 25. Annotations?
- 26. MetaLink
- 27. DEMO: Simple Link node := (ReflectivityExamples>>#exampleMethod) ast. link := MetaLink new metaObject: (Object new); selector: #halt. node link: link. ReflectivityExamples new exampleMethod
- 28. Meta Link • When setting link: • create twin if needed • install reflective method • On execution • generate code and execute, install CM
- 30. Link: metaobject The object to send a message to link := MetaLink new metaObject: [self halt]
- 31. Link: selector The selector to send link := MetaLink new ….. selector: #value
- 32. Link: control before, after, instead link := MetaLink new ….. control: #after
- 33. Link: control after: #ensure: wrap link := MetaLink new ….. control: #after
- 34. Link: control instead: last link wins (for now no AOP around) link := MetaLink new ….. control: #instead
- 35. Link: condition boolean or block link := MetaLink new ….. condition: [self someCheck]
- 36. Link: arguments what to pass to the meta?
- 37. Reifications • Every operation has data that it works on • Send: #arguments, #receiver, #selector • Assignment: #newValue, #name • All: #node, #object, #context
- 38. Link: arguments what to pass to the meta? link := MetaLink new ….. arguments: #(name newValue)
- 39. Reifications: condition link := MetaLink new condition: [: object | object == 1];
- 40. Virtual meta • Reifications can be the meta object link := MetaLink new metaObject: #receiver; selector: #perform:withArguments:; arguments: #(selector arguments).
- 41. Statement Coverage link := MetaLink new metaObject: #node; selector: #tagExecuted. “set this link on all the AST nodes" (ReflectivityExamples>>#exampleMethod) ast nodesDo: [:node | node link: link].
- 42. Users • BreakPoints Pharo5 • Coverage Kernel • ….
- 43. Everything is an Object
- 44. Everything is an object? SmalltalkImage classVarNamed: #CompilerClass ==> returns value Object binding class ==> Association
- 45. Why not an Object?
- 46. Globals/ClassVariables • We are close: bindings are associations • Add sublass “LiteralVariable” • Sublasses GlobalVariable, ClassVariable • Enhance API
- 48. Globals: Reflective APi global := SmalltalkImage classVariableNamed: #CompilerClass global read global write: someObject + helper methods + compatibility methods
- 49. Everything is an object? • Point instanceVariables • 5@3 instVarNamed: ‘x’ • 5@3 instVarNamed: ‘y’ put: 6
- 50. Why not an Object?
- 51. Slots Point slots (Point slotNamed: #x) read: (3@4) (Point slotNamed: #x) write: 7 to: (3@4)
- 52. Variables+MetaLink • Helper methods • But: can’t we annotate variables directly? Point assignmentNodes
- 53. Variables + Links • Object binding link: myMetaLink • (Point slotNamed: #x) link: myMetaLink (not yet in Pharo5)
- 54. Class Template Object subclass: #MyClass slots: { #x => WeakSlot } classVariables: { } category: 'Example'
- 55. Future • Can’t we model bit patterns and bind them to named virtual slots? • How to model Array-like layouts better?
- 56. Questions ?