Choose'10: Stephane Ducasse - Powerful DSL engineering in Smalltalk

Stéphane Ducasse

Stéphane [email protected]://stephane.ducasse.free.fr/

RMod

Powerful DSL engineering with Smalltalk

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A word of introduction

Reflective, metamodeler and happy programmer

Wrote several books on SmalltalkPharo by example, Squeak by Example, ...

Pushed Moose http://www.moosetechnology.org

Building Pharo http://www.pharo-project.org

Maintained Squeak http://www.squeak.org

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RMOD INRIA Team

Software evolution and software composition

Axis 1: Maintaining large software systemsMoose: a platform for reengineering, http://moosetechnology.com

Axis 2: Modular and Secure Reflective languages Revisiting fundamental aspects of OO languages Traits (SUN Microsystems...), ClassboxesPharo open-source Smalltalk http://www.pharo-project.orgStarting to work on a secure reflective languages

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Roadmap

A word about designSmalltalk an executable modeling languageInternal DSLs industrial examples

Mondrian GlamourSeaside

Helvetia: mastering embedded languagesTools: PetitParserConclusion

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About design and DSL

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Good OOP design makes implicit explicit

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Classes structure our vocabulary

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Classes are recipients of message reaction

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Boolean

xor:eqv:storeOn:and:or:ifTrue:ifFalse:&not |

False

and:or:ifTrue:ifFalse:&not |

True

and:or:ifTrue:ifFalse:&not |

ifTrue: trueAlternativeBlock ifFalse: falseAlternativeBlock

self subclassResponsibility


^ trueAlternativeBlock value


^ falseAlternativeBlock value

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Ternary logic

Boolean: true, false, unknown

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Focus on **your** domainDefine domain elements as first class objects

Long tradition in Smalltalk

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Exploratory modeling

Extreme/agile modeling

One domain expertOne developer

Pair-programming with the domain expertUsing the domain expert vocabulary

2007 SAP Experience with Smalltalk

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Requirements for a real DSL

Adequate syntaxCapture intent/domainEXECUTABLE!Tools

TestRunnerBrowsersSemantics versioningDebuggers!

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Smalltalk is a modeling executable language

Quite close from xactium

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Smalltalk

Modeling the worldSimple syntaxTrivial OO modelExecutable Full set of powerful tools

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A Simple and Pure Model

Everything is an object (no primitive)Only message passing (virtual)Public methods/Private attributesSingle inheritanceClass extension (Program slices)Closures

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Date today

is a unary message

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1000 factorial

is a unary message

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1 / 3

is a binary message

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1000 factorial / 999 factorial

is a unary/binary messages

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Color gray - Color white = Color black

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Color r: 0 g: 0 b: 1

is a keyword-based message

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From Java to Smalltalk

postman.send(mail,recipient);

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Removing


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Removing unnecessary

postman send mail recipient

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But without losing information

postman send mail to recipient

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postman send: mail to: recipient


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Tamagotchi

Small entityIts own night and day cycleEating, sleeping, been hungry, been satisfiedChanging color to indicate its mood

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Class

Object subclass: #Tamagotchi instanceVariableNames: ‘tummy hunger dayCount isNight' classVariableNames: '' poolDictionaries: '' category: ’TOMA'

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initialize“Initialize the internal state of a newly created tomagoshi”super initialize.tummy := 0.hunger := 2 atRandom + 1.self dayStart.self wakeUp

dayStart night := false. dayCount := 10

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timePass"Manage the night and day alternance and digestion"Beeper beep. dayCount := dayCount -1.dayCount isZero ifTrue:[ self nightOrDayEnd.

dayCount := 10]. self digest

digest"Digest slowly: every two cycle, remove one from the tummy”(dayCount isDivisibleBy: 2) ifTrue: [ tummy := tummy -1]

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Self-described

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Implemented totally in itself

extensible...

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Vocabulary points

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External Languages

Tools: make, flex, yaccData: awk, sed, XPath, Regular Expressions, SQL

+ expressive, full control- expensive to implement, no tools, hard to pass data around

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Internal Languages

Ruby: rspec, rakeJavaScript: jQuerySmalltalk: Mondrian, Seaside, PetitParser

+ easy to implement, tool support, easily mixable

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Embedded Languages

Language Workbenches: JetBrains MPS, Intentional Software

+ common infrastructure for different languages- new language, new tools, non-standard host language, targeted at domain experts (no programmers)

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Mondrian metaphor: painting a view

Composition with Red, Yellow and Blue Piet Mondrian (1921)

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Mondrian a scriptable visualization “language”fast brainstorming of ideasinteractive

developed by Girba/Meer (SCG, Bern), maintained, optimized by Bergel (Pleaid, Santiago, Chile)

heavily used by researchers in reengineeringpart of Moose

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The view consists of nodes and edges

view := ViewRenderer new.view nodes: classes.view edges: classes from: [:each | each superclass] to: [:each | each].view treeLayout.view open.

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Visual representation is given by the shape

view := ViewRenderer new.view borderedRectangleShape height: [:each | each numberOfMethods].view nodes: classes.view edges: classes

from: [:each | each superclass] to: [:each | each].

view treeLayout.view open.

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Blocks can be replaced by symbols

view := ViewRenderer new.view borderedRectangleShape height: #numberOfMethods.view nodes: classes.view edgesFrom: #superclass.view treeLayout.view open.

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Nesting is done through blocks

view := ViewRenderer new.view borderedRectangleShape.view nodes: classes forEach: [:each |

view nodes: each methods.view gridLayout].

view edgesFrom: #superclass.view treeLayout.view open.

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What about interaction?

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Interaction is scriptable, too

view := ViewRenderer new.view2 := ViewRenderer new.

view interaction onSelect: [:each | each viewOn: view2].view interaction popupView: [:each :aView | each viewOn: aView].

view nodes: ...

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Glamour

Internal language to build data explorer/browserComponent-based

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browser := GLMTabulator new.browser column: #one; column: #two.browser showOn: #one; using: [ browser table column: 'Character' evaluated: [ :each | each asString ]; column: 'ASCII' evaluated: [ :each | each asInteger printString ]; act: [:tree | tree inspect ] on: $i entitled: 'Inspect'; icon: [:x | MenuIcons helpIcon ]].browser showOn: #two; from: #one; using: [ browser text ].

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Seaside

To build dynamic applications Applications in production since 2002Natural FlowReusable statefull componentsSecure by defaultWeb 2.0http://www.seaside.st

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value1 := self request: ‘first number’.value2 := self request: ‘second number’.self inform: value1 asNumber + value2 asNumber

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Not concerned about HTTP

No manual request parsing

No XML configuration files

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Sour

ce: s

tock

.xch

ng, A

l Nak

ib

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html div id: ‘list’; with: [ html span class: ‘item’; with: ‘Item 1’. html span class: ‘item’; with: ‘Item 2’ ]

generates...<div id=”list”> <span class=”item”>Item 1</span> <span class=”item”>Item 2</span></div>

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html anchor callback: [ self inform: ‘Hello World’ ]; with: ‘Show Message’

Generates...

<a href=”/seaside/example1 ?_s=Ru8ZKgqjy0uDX3kf &_k=K5EQyqKE &32”>Show Message</a>

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WAComponent subclass: #Example2 instanceVariableNames: 'english' classVariableNames: '' poolDictionaries: '' category: 'SeaExample'

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renderContentOn: html html form: [ html button callback: [english := true]; text: 'english'. html button callback: [self inFrench]; text: 'french'. html submitButton callback: [ english ifFalse: [self inform: 'Bonjour'] ifTrue: [self inform: 'Hello'] ] ; text: 'Say Hello' ]

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Full hot on the fly debugFull integration with javascriptHandling of the back button...

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Slime

Rule for checking validation of Seaside internal language

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Mastering Embedded Languages

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!" #"$%&

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change semantics

introduce new syntax

change syntax & semantics

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Adopt, Extend, Overload

Package Name

x = 1

y = 1 (2, 1)

(2, 2)(1, 2)

x = 2

y = 2

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aBuilder row grow.aBuilder row fill.

aBuilder column grow.aBuilder column fill.

aBuilder x: 1 y: 1 add: (LabelShape new text: [ :each | each name ]; borderColor: #black; borderWidth: 1; yourself).aBuilder x: 1 y: 2 w: 2 h: 1 add: (RectangleShape new borderColor: #black; borderWidth: 1; width: 200;

Package Name

x = 1

y = 1 (2, 1)

(2, 2)(1, 2)

x = 2

y = 2

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row = grow.row = fill.

column = grow.column = fill.

(1 , 1) = label text: [ :each | each name ]; borderColor: #black; borderWidth: 1.

(1 , 2) - (2 , 1) = rectangle borderColor: #black; borderWidth: 1; width: 200; height: 100.

Package Name

x = 1

y = 1 (2, 1)

(2, 2)(1, 2)

x = 2

y = 2

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shape { cols: #grow, #fill; rows: #grow, #fill;}label { position: 1 , 1; text: [ :each | each name ]; borderColor: #black; borderWidth: 1;}rectangle { position: 1 , 2; colspan: 2; borderColor: #black; borderWidth: 1; width: 200;

Package Name

x = 1

y = 1 (2, 1)

(2, 2)(1, 2)

x = 2

y = 2

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Homogeneous Tools

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Domain-Specific

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Traditional Smalltalk Compiler

Smalltalk

Parser

Semantic

Analysis

Bytecode

Generation

Executable

Code

Source

Code


Smalltalk

Parser

Semantic

Analysis

Bytecode

Generation

Executable

Code

Source

Code

<parse> <transform> <attribute> <bytecode>

Rules


Smalltalk

Parser

Semantic

Analysis

Bytecode

Generation

Executable

Code

Source

Code


Rules

<complete> <highlight>......


Smalltalk

Parser

Semantic

Analysis

Bytecode

Generation

Executable

Code

Source

Code


Rules

Pidgin path

Creole path

<complete> <highlight>......

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Scannerless Parsers combine what is usually done by two independent tools (scanner and parser) into one. This makes writing a grammar much simpler and avoids common problems when grammars are composed.

Parser Combinators are building blocks for parsers modeled as a graph of composable objects; they are modular and maintainable, and can be changed, recomposed, transformed and reflected upon.

Parsing Expression Grammars (PEGs) provide ordered choice. Unlike in parser combinators, the ordered choice of PEGs always follows the first matching alternative and ignores other alternatives. Valid input always results in exactly one parse-tree, the result of a parse is never ambiguous.

Packrat Parsers give linear parse time guarantees and avoid common problems with left-recursion in PEGs.

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BNFID ::= letter { letter | digit } ;

Ometa2id = letter (letter | digit)*

PetitParserid := #letter asParser ,! (#letter asParser / #digit asParser) star

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Smalltalk is a serious player in DSL

Trivial modelTrivial syntax

Internal DSLsEmbedded DSLsFull tool supportExtensible (build your own)Executable

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Choose'10: Stephane Ducasse - Powerful DSL engineering in Smalltalk

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