IWST 2105 Video: https://www.youtube.com/watch?v=bHAhiV8VajQ

1. Code Transformation by
Direct Transformation of ASTs
M. Rizun, J.-C. Bach, S. Ducasse
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2. Example of simple code transformation
foo
| result a b |
a := 2.
b := 3.
result := a >= b
ifTrue: [ a ]
ifFalse: [ b ]
foo
| result a b |
a := 2.
b := 3.
result := a max: b
Source code Resulting code
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transformation

3. Manual code transformation process
(in big system)
Replace all found occurrences by target code.
Search for all occurrences of the code to replace in the source code.
Definition of the desired target code. (RHS)
Definition of the code to change. (LHS)
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4. Find & Replace
“…code…”
x >= y
ifTrue: [ x ]
ifFalse: [ y ]
“…code…”
“…code…”
x max: y
“…code…”
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Right-Hand Side partLeft-Hand Side part

5. Problems
Time-consuming and annoying task.
Complex and error-prone process.
Rules are not reusable.
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6. Tools to automate process
Tool Create transformation rules.
Apply rules on desired environment scope.
Save rules for later reuse.
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7. Rewrite Engine
Engine for code
transformation
Unintuitive
syntax & no GUI
to apply rules
Pros
Cons
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8. “Scary” transformation rule
Left-Hand Side part
| `@temporaries |
`.InitializationStatement.
`@condition1
ifTrue: [
| `@otherTemporaries |
`@.Statements.
`@condition2
ifTrue: [ ``@value := ``@calculate ]
ifFalse: [ ``@value := `#wrongLiteral ] ]
Right-Hand Side part
| `@temporaries `@otherTemporaries |
`.InitializationStatement.
`@condition1
ifFalse: [ ^self ].
`@.Statements.
``@value := `@condition2
ifTrue: [ ``@calculate ]
ifFalse: [ `#wrongLiteral ]
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9. Inattention causes impactful mistakes!
`.InitializationStatement `InitializationStatement
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How to apply rules?

11. OR
| rule result aCollection anEnvironment |
aCollection := self environment.
anEnvironment := RBClassEnvironment
classes: aCollection.
rule := (Smalltalk globals at: self rules
selectedItem) new.
result := RBSmalllintChecker
runRule: rule
onEnvironment: anEnvironment.
(ChangesBrowser changes: result builder
changes) open
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12. Rewrite Tool
´ Intuitive GUI
´ Real time result
´ Apply rules to any scope you want
´ Save rules for later reuse
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13. A. Input code
B. Resulting code
C. LHS part of rule
D. RHS part of rule
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15. 15
Live Demo

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Download & Info
´ http://smalltalkhub.com/#!/~MarkRizun/RewriteTool
´ Configuration Browser (Pharo4)
´ http://myfuncoding.com
´ Pharo For The Enterprise (RewriteTool chapter)
https://github.com/SquareBracketAssociates/PharoForTheEnterprise-english/tree/master/RewriteTool

17. Mark Rizun e-mail: mrizun@gmail.com blog: http://myfuncoding.blogspot.com/
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