martin fowler dsl-intro

7/30/2019 Martin Fowler Dsl-Intro

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IntroducingDomain Specific

LanguagesMARTIN FOWLER

http://martinfowler.com

1Tuesday, April 7, 2009
http://martinfowler.com/http://martinfowler.com/http://martinfowler.com/


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DSLs are everywhere

graphviz

ant

rakeLINQ

Hibernate Query Language

regular expressions

FITSQL

struts-config.xmlJMock expectations

rails validationsmake

CSS



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Should they be used more often?

Can they be done better?



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Close the door

Open the seconddraw down

Turn on thebedside light

Opening the door resets thesystem and locks the panel

Opening my Secret Panel



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State

Machine

Transition

name

State

1 1source target

namecode

Abstract Event

Command

Event

!

action

! !

!

1

trigger!

1 start

!

!reset events



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Event doorClosed = new Event("doorClosed", "D1CL");

Event drawOpened = new Event("drawOpened", "D2OP");Event lightOn = new Event("lightOn", "L1ON");

Event doorOpened = new Event("doorOpened", "D1OP");Event panelClosed = new Event("panelClosed", "PNCL");

Command unlockPanelCmd = new Command("unlockPanel", "PNUL");Command lockPanelCmd = new Command("lockPanel", "PNLK");Command lockDoorCmd = new Command("lockDoor", "D1LK");

Command unlockDoorCmd = new Command("unlockDoor", "D1UL");

machine.addResetEvents(doorOpened);

State idle = new State("idle");State activeState = new State("active");

State waitingForLightState = new State("waitingForLight");

State waitingForDrawState = new State("waitingForDraw");State unlockedPanelState = new State("unlockedPanel");

StateMachine machine = new StateMachine(idle);

idle.addTransition(doorClosed, activeState);idle.addAction(unlockDoorCmd);

idle.addAction(lockPanelCmd);

activeState.addTransition(drawOpened, waitingForLightState);activeState.addTransition(lightOn, waitingForDrawState);

waitingForLightState.addTransition(lightOn, unlockedPanelState);

waitingForDrawState.addTransition(drawOpened, unlockedPanelState);

unlockedPanelState.addAction(unlockPanelCmd);

unlockedPanelState.addAction(lockDoorCmd);

unlockedPanelState.addTransition(panelClosed, idle);



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events

doorClosed D1CLdrawOpened D2OP

lightOn L1ONdoorOpened D1OP

panelClosed PNCL

end

resetEvents

doorOpenedend

commands

unlockPanel PNULlockPanel PNLK

lockDoor D1LK

unlockDoor D1UL

end

state idle

actions {unlockDoor lockPanel}doorClosed => active

end

state active

drawOpened => waitingForLight

lightOn => waitingForDrawend

state waitingForLight

lightOn => unlockedPanelend

state waitingForDraw

drawOpened => unlockedPanel

end

state unlockedPanel

actions {unlockPanel lockDoor}

panelClosed => idleend



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event :doorClosed, "D1CL"

event :drawOpened, "D2OP"event :lightOn, "L1ON"

event :doorOpened, "D1OP"

event :panelClosed, "PNCL"

command :unlockPanel, "PNUL"

command :lockPanel, "PNLK"command :lockDoor, "D1LK"

command :unlockDoor, "D1UL"

resetEvents :doorOpened

state :idle do

actions :unlockDoor, :lockPaneltransitions :doorClosed => :active

end

state :active dotransitions :drawOpened => :waitingForLight,

:lightOn => :waitingForDrawend

state :waitingForLight do

transitions :lightOn => :unlockedPanelend

state :waitingForDraw do

transitions :drawOpened => :unlockedPanelend

state :unlockedPanel doactions :unlockPanel, :lockDoor

transitions :panelClosed => :idle

end



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state idleactions {unlockDoor lockPanel}

doorClosed => active

end

state :idle doactions :unlockDoor, :lockPanel

transitions :doorClosed => :active

end

External DSL Internal DSL(aka Embedded DSL)

XML as carr ier syntax11Tuesday, April 7, 2009


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public class BasicStateMachine extends StateMachineBuilder {

Events doorClosed, drawOpened, lightOn, panelClosed;

Commands unlockPanel, lockPanel, lockDoor, unlockDoor;

States idle, active, waitingForLight, waitingForDraw, unlockedPanel;ResetEvents doorOpened;

protected void defineStateMachine() {

doorClosed. code("D1CL");

drawOpened. code("D2OP");lightOn. code("L1ON");panelClosed.code("PNCL");

doorOpened. code("D1OP");

unlockPanel.code("PNUL");

lockPanel. code("PNLK");lockDoor. code("D1LK");

unlockDoor. code("D1UL");

idle.actions(unlockDoor, lockPanel)

.transition(doorClosed).to(active);

active

.transition(drawOpened).to(waitingForLight)

.transition(lightOn). to(waitingForDraw);

waitingForLight.transition(lightOn).to(unlockedPanel)

;

waitingForDraw

.transition(drawOpened).to(unlockedPanel);

unlockedPanel.actions(unlockPanel, lockDoor)

.transition(panelClosed).to(idle);

}}



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State idle = new State("idle");

State activeState = new State("active");idle.addTransition(doorClosed, activeState);

idle.addAction(unlockDoorCmd);

idle.addAction(lockPanelCmd);

activeState.addTransition(drawOpened, waitingForLightState);

activeState.addTransition(lightOn, waitingForDrawState);

idle

.actions(unlockDoor, lockPanel)

.transition(doorClosed).to(active)

;

active

.transition(drawOpened).to(waitingForLight)

.transition(lightOn). to(waitingForDraw)

;

Command-Query API

Fluent API



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Domain Specific Language (noun)

a computer programming language of limitedexpressiveness focused on a particular domain

languagecomputer programming

limited expressivenessfocused on a particular domain



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DSL

Script Parse

Semantic Model

Execute

Generate

Code

optional



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Oslo

DSL Tools

Charles Simonyi

made Intel liJ andReSharper

open source

eclipsemature

Language Workbenches



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Source Editing

javac hal.java



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Model Repository

generate

Projectional Editing

projections



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Source Projectional

DSL Tools

Diagrams

Structured Text

Oslo



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input =~ /\d{3}-\d{3}-\d{4}/



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p.question {

font-style: italic;

font-weight: bold;

}

p.answer { padding: 0 0 0 1em }



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write

read23Tuesday, April 7, 2009


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For more information...http://www.martinfowler.com/bliki/DomainSpecificLanguage.html

MARTIN

FOWLER

http://martinfowler.com
http://martinfowler.com/http://martinfowler.com/http://www.martinfowler.com/bliki/DomainSpecificLanguage.htmlhttp://www.martinfowler.com/bliki/DomainSpecificLanguage.html

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