Going to Mars with Groovy Domain-Specific Languages

Groovy
Domain
Specific Guillaume Laforge
Groovy Project Manager
SpringSource / VMware
Languages @glaforge

1

Guillaume Laforge

• Groovy Project Manager at VMware
•Initiator of the Grails framework
•Creator of the Gaelyk
and Caelyf toolkits

• Co-author of Groovy in Action

• Follow me on...
•My blog: http://glaforge.appspot.com
•Twitter: @glaforge
•Google+: http://gplus.to/glaforge
3

Introduction
Deﬁnition, Examples, Goals, Pros & Cons

4

Domain-Specific Languages

• Wikipedia definition

{ }
A Domain-Specific Language is a programming
language or executable specification language that
offers, through appropriate notations and
abstractions, expressive power focused on, and usually
restricted to, a particular problem domain.

• In contrast to General Purprose Languages
• Also known as: fluent / human interfaces, language oriented programming,
little or mini languages, macros, business natural languages...

5

Technical examples
Glade XSLT
<?xml version="1.0"?> <?xml version="1.0"?>
<GTK-Interface> <xsl:stylesheetversion="1.0"
<widget> xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<class>GtkWindow</class> <xsl:output method="xml"/>
<name>HelloWindow</name> <xsl:template match="*">
<border_width>5</border_width>
<Signal>
<xsl:element name="{name()}"> Regex
<xsl:for-each select="@*">
<name>destroy</name>
<handler>gtk_main_quit</handler>
<xsl:element name="{name()}">
<xsl:value-of select="."/>
"x.z?z{1,3}y"
</Signal>
<title>Hello</title> </xsl:element>
<type>GTK_WINDOW_TOPLEVEL</type> </xsl:for-each>
<position>GTK_WIN_POS_NONE</position> <xsl:apply-templates select="*|text()"/>
<allow_shrink>True</allow_shrink> </xsl:element>
<allow_grow>True</allow_grow> </xsl:template>
<auto_shrink>False</auto_shrink> </xsl:stylesheet>
<widget>
<class>GtkButton</class>
<name>Hello World</name>
<can_focus>True</can_focus>
fetchmail
<label>Hello World</label>
# Poll this site first each cycle.
</widget> poll pop.provider.net proto pop3
</widget> user "jsmith" with pass "secret1" is "smith" here
</GTK-Interface> user jones with pass "secret2" is "jjones" here with options keep

SQL # Poll this site second, unless Lord Voldemort zaps us first.
poll billywig.hogwarts.com with proto imap:
user harry_potter with pass "floo" is harry_potter here
SELECT * FROM TABLE
# Poll this site third in the cycle.
WHERE NAME LIKE '%SMI' # Password will be fetched from ~/.netrc
ORDER BY NAME poll mailhost.net with proto imap:
user esr is esr here

Antimalaria drug Insurance policy risk HR skills representation
resistance simulation calculation engine

Nuclear safety simulations

Market data feeds analysis Loan acceptance rules engine

Goals of DSLs

• Use a more expressive language than a general-purpose one

• Share a common metaphor of understanding
between developers and subject matter experts

• Have domain experts help with the design
of the business logic of an application

• Avoid cluttering business code with too much boilerplate technical code
thanks to a clean separation

• Let business rules have their own lifecycle

8

Pros and cons

Pros Cons
• Domain experts can help, validate, • Learning cost vs. limited applicability
modify, and often develop DSL
programs
• Cost of designing, implementing &
maintaining DSLs as well as tools/IDEs
• Somewhat self-documenting
• Attaining proper scope
• Enhance quality, productivity,
• Trade-offs between domain speciﬁcity
reliability, maintainability, portability, and general purpose language
reusability constructs
• Safety; as long as the language
• Efﬁciency cost
constructs are safe, any DSL
sentence can be considered safe • Proliferation of similar
non-standard DSLs

9

Groovy provides...

• A ﬂexible and malleable syntax
•scripts, native syntax constructs (list, map, ranges), closures, less punctuation...

• Compile-time and runtime meta-programming
•metaclasses, AST transformations
•also operator overloading

• The ability to easily integrate into Java / Spring apps
•also security and safety

10

Let’s get started!

11

Your mission: build a DSL for
a Mars robot

We need a robot!
class!Robot!{}

14

It should move...
class!Robot!{
!!!!void)move()!{}
}

15

..in a direction!
class!Robot!{
!!!!void)move(String!dir)!{}
}

16

More explicit direction
class!Robot!{
!!!!void)move(Direction!dir)!{}
}

enum!Direction!{
!!!!left,!right,!forward,!backward
}

17

Now how can we control it?

import)static)mars.Direction.*;
import)mars.Robot;

public)class)Command!{
))))public)static)void)main(String[]!args)!{
!!!!!!!!Robot!robot!=)new!Robot();
!!!!!!!!robot.move(left);
!!!!}
}

18


import)mars.Robot;

!!!!}
} Syntactical
noise!

18


))))))))))))))))))))))))))))))—
)))))))))))))))))—
import)mars.Robot;

——————————————————————
))))————————————————————————————————————————
))))))))—————))))))))))))))))))))—
))))))))))))))))))—))))——
))))—
!!!!}
—
} Syntactical
noise!

18

Scripts vs Classes
Optional semicolons & parens
import)static)mars.Direction.*
import)mars.Robot

!!!!!!!!def))!robot!=)new!Robot()
!!!!!!!!robot.move!left

19

Scripts vs Classes
import)mars.Robot

Optional typing


19

Scripts vs Classes
import)mars.Robot

Optional typing


But I don’t want to
compile a script for
every command!
19

GroovyShell to the rescue

21

def$shell%=$new%GroovyShell()
shell.evaluate(
%%%%new%File("command.groovy")
)

21

shell.evaluate(
integration.groovy %%%%new%File("command.groovy")
)

21

shell.evaluate(
)

import$static$mars.Direction.*
import$mars.Robot

def$robot%=$new%Robot()
robot.move%left
21

shell.evaluate(
)

import$static$mars.Direction.*
import$mars.Robot
command.groovy
def$robot%=$new%Robot()
robot.move%left
21

Integration mechanisms

• Different solutions available:
•Groovy’s own mechanisms
• GroovyScriptEngine, Eval,
GroovyClassLoader, GroovyShell
•Java 6: javax.script.* / JSR-223
•
Groovy provides a JSR-223 implementation
•Spring’s lang namespace

• Groovy provides the highest level of ﬂexibility
and customization, but JSR-223 is a standard...

22

What’s wrong with our DSL?

import)mars.Robot

def)robot!=)new!Robot()
robot.move!left

23

Can’t we hide
those imports?

import)mars.Robot

robot.move!left

23

Can’t we hide
those imports?

import)mars.Robot

robot.move!left
Can’t we inject
the robot?

23

Can’t we hide
those imports?

import)mars.Robot

robot.move!left
Can’t we inject
Do we really need to the robot?
repeat ‘robot’?
23

I’m sorry Dave,
you can’t do that!

What we really want is...

!move!left!

25

Let’s inject a robot!

• We can pass data in / out of scripts through the Binding
•it’s basically just like a map of variable name keys and their associated values

26



def)binding!=)new!Binding([
!!!!robot:!new!Robot()
])
def)shell!=)new!GroovyShell(binding)
shell.evaluate(
!!!!new!File("command.groovy")
)

26



integration.groovy
!!!!robot:!new!Robot()
])
shell.evaluate(
)

26

Better?


robot.move!left

27

Better?
Robot import
removed

robot.move!left

27

Better?
Robot import
removed

robot.move!left

Robot injected,
no ‘new’ needed

27

How to inject the direction?

• Using the binding...
!!!!robot:!new!Robot(),
!!!!left:!!!!!Direction.left,
!!!!right:!!!!Direction.right,
!!!!backward:!Direction.backward,
!!!!forward:!!Direction.forward
])
shell.evaluate(
)
28

Fragile in case of
new directions!
!!!!left:!!!!!Direction.left,
!!!!right:!!!!Direction.right,
!!!!backward:!Direction.backward,
!!!!forward:!!Direction.forward
])
shell.evaluate(
)
28


!!!!*:!Direction.values()
!!!!!!!!!!!!.collectEntries!{
!!!!!!!!!!!!!!!![(it.name()):!it]
!!!!!!!!!!!!}
])
shell.evaluate(
)
29


• Using compiler customizers...

• Let’s have a look at them

30

Compilation customizers

• Ability to apply some customization
to the Groovy compilation process

• Three available customizers
•ImportCustomizer: add transparent imports
•ASTTransformationCustomizer: injects an AST transform
•SecureASTCustomizer: restrict the groovy language to an allowed subset

• But you can implement your own

31

Imports customizer

new!GroovyShell(new!Binding([robot:!new)Robot()]))
!!!!.evaluate("import!static!Direction.*n"!+
!!!!!!!!!!!!!!"robot.move!left")

32

Imports customizer

Cheat with string
concatenation? Bad!

new!GroovyShell(new!Binding([robot:!new)Robot()]))
!!!!.evaluate("import!static!Direction.*n"!+
!!!!!!!!!!!!!!"robot.move!left")

32

Imports customizer
def!configuration!=!new!CompilerConfiguration()
!
def!imports!=!new!ImportCustomizer()
imports.addStaticStar(mars.Direction.name)
configuration.addCompilationCustomizers(imports)!
!

new!GroovyShell(new!Binding([robot:!new)Robot()]),!!!!!!!
!
!!!!!!!!!!!!!!!!configuration)
!!!!.evaluate("robot.move!left")!!!!!!

33

AST transformation customizer
!
configuration.addCompilationCustomizers(imports,
!!!!!!!!!!!!!new!ASTTransformationCustomizer(Log))
!
!
!!!!.evaluate("robot.move!left"!+!"n"
!!!!!!!!!!!!!!"log.info!‘Robot!moved’")!!!!!!!!!!!

34

AST transformation customizer
!
configuration.addCompilationCustomizers(imports,
!!!!!!!!!!!!!new!ASTTransformationCustomizer(Log))
!
!
!!!!.evaluate("robot.move!left"!+!"n"
!!!!!!!!!!!!!!"log.info!‘Robot!moved’")!!!!!!!!!!!
@Log injects a logger in
scripts and classes
34

Secure the onboard
trajectory calculator

Secure AST customizer
Idea: Secure the rocket’s onboard trajectory
calculation system by allowing only math
expressions to be evaluated by the calculator

• Let’s setup our environment
•an import customizer to import java.lang.Math.*
•prepare a secure AST customizer

def%imports%=%new%ImportCustomizer().addStaticStars('java.lang.Math')
def%secure%=%new%SecureASTCustomizer()

36

...
secure.with!{
//!disallow!closure!creation
closuresAllowed!=!false!
//!disallow!method!definitions
methodDefinitionAllowed!=!false!
!
//!empty!white!list!=>!forbid!imports
importsWhitelist!=![]!
staticImportsWhitelist!=![]
//!only!allow!the!java.lang.Math.*!static!import
staticStarImportsWhitelist!=!['java.lang.Math']
...

37

Disallow closures
... and methods
secure.with!{
!
...

37

Disallow closures
... and methods
secure.with!{
//!disallow!method!definitions Black / white list
imports
!
...

37

...
//%language%tokens%allowed
tokensWhitelist%=%[
PLUS,%MINUS,%MULTIPLY,%DIVIDE,%MOD,%POWER,%PLUS_PLUS,%MINUS_MINUS,%
COMPARE_EQUAL,%COMPARE_NOT_EQUAL,%COMPARE_LESS_THAN,%COMPARE_LESS_THAN_EQUAL,%
COMPARE_GREATER_THAN,%COMPARE_GREATER_THAN_EQUAL
]
%
//%types%allowed%to%be%used%(including%primitive%types)
constantTypesClassesWhiteList%=%[
Integer,%Float,%Long,%Double,%BigDecimal,%
Integer.TYPE,%Long.TYPE,%Float.TYPE,%Double.TYPE
]
%
//%classes%who%are%allowed%to%be%receivers%of%method%calls
receiversClassesWhiteList%=%[%
Math,%Integer,%Float,%Double,%Long,%BigDecimal%]
}
...
38

Secure AST customizer You can build a subset of
the Groovy syntax!
...
tokensWhitelist%=%[
]
%
constantTypesClassesWhiteList%=%[
]
%
}
...
38

Secure AST customizer You can build a subset of
the Groovy syntax!
...
tokensWhitelist%=%[
]
%
Black / white list
constantTypesClassesWhiteList%=%[ usage of classes
]
%
}
...
38


• Ready to evaluate our ﬂight equations!
def%config%=%new%CompilerConfiguration()
config.addCompilationCustomizers(imports,%secure)

def%shell%=%new%GroovyShell(config)
%
shell.evaluate%'cos%PI/3'

• But the following would have failed:

shell.evaluate%'System.exit(0)'

39

Back to our robot...

robot.move)left

40

Back to our robot...

Still need to get rid
of the robot prefix!

robot.move)left

40

Can we remove it?

да !

How to remove the ‘robot’?

• Instead of calling the move() method on the robot
instance, we should be able to call the move() method
directly from within the script

• Two approaches:

• Inject a ‘move’ closure in the • Use a base script class with a
‘move’ method delegating to the
binding with a method pointer
robot

42

Inject a closure in the binding
def$robot%=%new%Robot()
binding%=$new%Binding([
%%%%robot:%robot,
%%%%*:%Direction.values()
%%%%%%%%%%%%.collectEntries%{
%%%%%%%%%%%%%%%%[(it.name()):%it]
%%%%%%%%%%%%},

%%%%move:%robot.&move
])

43

Inject a closure in the binding
def$robot%=%new%Robot()
binding%=$new%Binding([
%%%%robot:%robot,
%%%%*:%Direction.values()
%%%%%%%%%%%%.collectEntries%{
%%%%%%%%%%%%%%%%[(it.name()):%it]
%%%%%%%%%%%%},

%%%%move:%robot.&move
])
Method pointer (a closure) on
robot’s move instance method
43

Define a base script class

abstract)class!RobotBaseScriptClass!!!
!!!!!!!extends!Script!{
!!!!void!move(Direction!dir)!{
!!!!!!!!def)robot!=!this.binding.robot
!!!!!!!!robot.move!dir
!!!!}
}

44


!!!!}
}

The move() method is
now at the script level

44


!!!!}
}

The move() method is Access the robot through
now at the script level the script’s binding

44

Configure the base script class

def)conf)=)new)CompilerConfiguration()
conf.scriptBaseClass)=)RobotBaseScriptClass

45

Configure the base script class

def)conf)=)new)CompilerConfiguration()
conf.scriptBaseClass)=)RobotBaseScriptClass

Scripts evaluated with
this configuration will
inherit from that class

45

Ready for lift off!

%%move%left

Beep, beep...
yes but how do you
define the speed?
...beep...

What we could do now is...

move!left,!at:!3.km/h

49


Mix of named and
normal parameters


49


Mix of named and
normal parameters


How to add a km
property to numbers?

49

Adding properties to numbers

• We need to:

• deﬁne units, distance and speed

• have a nice notation for them
• that’s where we add properties to numbers!

50

Unit enum and Distance class
enum$DistanceUnit%{
%%%%centimeter%('cm',%%%%0.01),
%%%%meter%%%%%%(%'m',%%%%1),%
%%%%kilometer%%('km',%1000)%
%%%%
%%%%String%abbreviation
%%%%double%multiplier
%%%%
%%%%Unit(String%abbr,%double%mult)%{
%%%%%%%%this.abbreviation%=%abbr
%%%%%%%%this.multiplier%=%mult%
%%%%}

%%%%String%toString()%{%abbreviation%}%
}
51

Unit enum and Distance class
@TupleConstructor%
enum$DistanceUnit%{ class%Distance%{
%%%%centimeter%('cm',%%%%0.01), %%%%double%amount%
%%%%meter%%%%%%(%'m',%%%%1),% %%%%DistanceUnit%unit
%%%%kilometer%%('km',%1000)%
%%%% %%%%String%toString()%{%
%%%%String%abbreviation %%%%%%%%"$amount%$unit"%
%%%%double%multiplier %%%%}%
%%%% }
%%%%Unit(String%abbr,%double%mult)%{
%%%%}

}
51

Different techniques

• To add dynamic methods or properties,
there are several approaches at your disposal:
• ExpandoMetaClass
• custom MetaClass
• Categories

• Let’s have a look at the ExpandoMetaClass

52

Using ExpandoMetaClass

Number.metaClass.getCm%=%{%f>%
%%%%new%Distance(delegate,%Unit.centimeter)%
}
Number.metaClass.getM%=%{%f>%
%%%%new%Distance(delegate,%Unit.meter)%
}
Number.metaClass.getKm%=%{%f>%
%%%%new%Distance(delegate,%Unit.kilometer)%
}

53

Add that to
integration.groovy

}
}
}

53

Add that to
integration.groovy

}
}
}

‘delegate’ is the
current number
53

Add that to
integration.groovy Usage in
your DSLs
} 40.cm!
3.5.m
} 4.km
}

‘delegate’ is the
current number
53

Distance okay, but speed?

• For distance, we just added a property access after the number,
but we now need to divide (‘div’) by the time

2.km/h

54



The div() method
on Distance

2.km/h

54



The div() method
on Distance

2.km/h
An h duration
instance in the binding
54

First, let’s look at time
enum$TimeUnit%{
%%%%hour%%%%%%('h',%%%3600),
%%%%minute%%%%('min',%%%60),%
%%%%kilometer%('s',%%%%%%1)%
%%%%
%%%%String%abbreviation
%%%%double%multiplier
%%%%
%%%%TimeUnit(String%abbr,%double%mult)%{
%%%%}

}
55

First, let’s look at time @TupleConstructor%
class%Duration%{
enum$TimeUnit%{ %%%%double%amount%
%%%%hour%%%%%%('h',%%%3600), %%%%TimeUnit%unit
%%%%minute%%%%('min',%%%60),%
%%%%kilometer%('s',%%%%%%1)% %%%%String%toString()%{%
%%%% %%%%%%%%"$amount%$unit"%
%%%%String%abbreviation %%%%}%
%%%%double%multiplier }
%%%%
%%%%TimeUnit(String%abbr,%double%mult)%{
%%%%}

}
55

Inject the ‘h’ hour constant in the binding

!!!!*:!Direction.values()
!!!!!!!!!!!!.collectEntries!{
!!!!!!!!!!!!!!!![(it.name()):!it]
!!!!!!!!!!!!},

!!!!h:!new!Duration(1,!TimeUnit.hour)
])

56

Now at (light!) speed
@TupleConstructor)
class)Speed){
))))Distance)distance
))))Duration)duration

))))String)toString()){)
))))))))"$distance/$duration")
))))})
}

57

Operator overloading
a%+%b%%//%a.plus(b)
a%f%b%%//%a.minus(b) • Currency amounts
a%*%b%%//%a.multiply(b) • 15.euros + 10.dollars
a%/%b%%//%a.div(b)
a%%%b%%//%a.modulo(b) • Distance handling
a%**%b%//%a.power(b) • 10.km - 10.m
a%|%b%%//%a.or(b)
a%&%b%%//%a.and(b) • Workﬂow, concurrency
a%^%b%%//%a.xor(b) • taskA | taskB & taskC
a[b]%%%//%a.getAt(b)
a%<<%b%//%a.leftShift(b) • Credit an account
a%>>%b%//%a.rightShift(b)
+a%%%%%//%a.unaryPlus()
• account << 10.dollars
account += 10.dollars
fa%%%%%//%a.unaryMinus() account.credit 10.dollars
~a%%%%%//%a.bitwiseNegate()

58


• Update the Distance class with a div() method
following the naming convetion for operators

class%Distance%{
%%%%...
%%%%Speed%div(Duration%t)%{
%%%%%%%%new%Speed(this,%t)
%%%%}
%%%%...
}

59


• Update the Distance class with a div() method
following the naming convetion for operators

class%Distance%{
%%%%...
%%%%Speed%div(Duration%t)%{
%%%%%%%%new%Speed(this,%t)
%%%%}
%%%%...
} Optional return

59

Equivalence of notation

• Those two notations are actually equivalent:

2.km/h

2.getKm().div(h)

60

Equivalence of notation

• Those two notations are actually equivalent:

2.km/h
This one might be
slightly more verbose!

2.getKm().div(h)

60

Named parameters usage

61


Normal
parameter

61


Normal Named
parameter parameter

61


Normal Named
parameter parameter
Will call:
def!take(Map!m,!Direction!q)

61


Normal Named
parameter parameter
Will call:

All named parameters go
into the map argument
61


Normal Named
parameter parameter
Will call:

All named parameters go Positional parameters
into the map argument come afterwards
61


62


Can we get rid of
the comma?

62


Can we get rid of What about the
the comma? colon too?

62

Command chains

• A grammar improvement in Groovy 1.8 allowing you
to drop dots & parens when chaining method calls
• an extended version of top-level statements like println

• Less dots, less parens allow you to
•write more readable business rules
•in almost plain English sentences
•
(or any language, of course)

63

Command chains

%move%left%%at%3.km/h%

64

Command chains
Alternation of
method names


64

Command chains
Alternation of
method names


and parameters
(even named ones)

64

Command chains

Equivalent to:

%%%%%(%%%%).%%(%%%%%%)

64

Look Ma!
No par ens,
no dots!

Command chains
//%Java%fluent%API%approach
class%Robot%{
%%%%...
$$$$def%move(Direction%dir)%{
%%%%%%%%this.dir%=%dir
%%%%%%%%return%this
%%%%}

%%%%def%at(Speed%speed)%{
%%%%%%%%this.speed%=%speed
%%%%%%%%return%this
%%%%}
%%%%...
}
66

Command chains
def)move(Direction)dir)){
))))[at:){)Speed)speed)F>
))))))))))))...
))))))))}]
))))}]
}

67

Command chains
))))))))))))... Nested maps
))))))))}] and closures
))))}]
}

67

Command chains
))))))))))))... Nested maps
))))))))}] and closures
))))}]
}

Usage in
your DSLs move%left%at%3.km/h

67

Command chains
//%methods%with%multiple%arguments%(commas)

68

Command chains
take%coffee%%with%sugar,%milk%%and%liquor

68

Command chains

//%leverage%namedfargs%as%punctuation

68

Command chains

check%that:%vodka%%tastes%good

68

Command chains


//%closure%parameters%for%new%control%structures

68

Command chains


given%{}%%when%{}%%then%{}

68

Command chains



//%zerofarg%methods%require%parens

68

Command chains



select%all%%unique()%from%names

68

Command chains




//%possible%with%an%odd%number%of%terms

68

Command chains




deploy%left%%arm
68

Command chains
%%%%(%%%%%%).%%%%(%%%%%%%%%%%).%%%(%%%%%%)




deploy%left%%arm
68

Command chains
%%%%(%%%%%%).%%%%(%%%%%%%%%%%).%%%(%%%%%%)

%%%%%(%%%%%%%%%%%).%%%%%%(%%%%)



deploy%left%%arm
68

Command chains
%%%%(%%%%%%).%%%%(%%%%%%%%%%%).%%%(%%%%%%)

%%%%%(%%%%%%%%%%%).%%%%%%(%%%%)

%%%%%(%%).%%%%(%%).%%%%(%%)


deploy%left%%arm
68

Command chains
%%%%(%%%%%%).%%%%(%%%%%%%%%%%).%%%(%%%%%%)

%%%%%(%%%%%%%%%%%).%%%%%%(%%%%)

%%%%%(%%).%%%%(%%).%%%%(%%)

%%%%%%(%%%).%%%%%%%%.%%%%(%%%%%)

deploy%left%%arm
68

Command chains
%%%%(%%%%%%).%%%%(%%%%%%%%%%%).%%%(%%%%%%)

%%%%%(%%%%%%%%%%%).%%%%%%(%%%%)

%%%%%(%%).%%%%(%%).%%%%(%%)

%%%%%%(%%%).%%%%%%%%.%%%%(%%%%%)

deploy%left%%arm
%%%%%%(%%%%).
68

Final result

move!forward!at!3.km/h

69

move forward
at 3.km/h Yes! We did it!

What about security
and safety?

Security and safety
JVM Security Managers
SecureASTCustomizer
Sandboxing
Controlling scripts execution

72

Playing it safe...

• You have to think carefully about
what DSL users are allowed to do with your DSL

• Forbid things which are not allowed
•leverage the JVM’s Security Managers
•
this might have an impact on performance
•use a Secure AST compilation customizer
•
not so easy to think about all possible cases
•avoid long running scripts with *Interrupt transformations

74

Security Managers

• Groovy is just a language leaving on the JVM,
so you have access to the usual Security Managers mechanism
• Nothing Groovy speciﬁc here
• Please check the documentation on Security Managers
and how to design policy ﬁles

75

SecureASTCustomizer
def!secure!=!new!SecureASTCustomizer()
secure.with!{
!!!closuresAllowed!=!false!
!!!methodDefinitionAllowed!=!false!
//!empty!white!list!=>!forbid!certain!imports
!!!importsWhitelist!=![...]!
!!!staticImportsWhitelist!=![...]
//!only!allow!some!static!import
!!!staticStarImportsWhitelist!=![...]
//!language!tokens!allowed
!!!!tokensWhitelist!=![...]
//!types!allowed!to!be!used
!!!constantTypesClassesWhiteList!=![...]
//!classes!who!are!allowed!to!be!receivers!of!method!calls
!!!receiversClassesWhiteList!=![...]
}
def!config!=!new!CompilerConfiguration()
config.addCompilationCustomizers(secure)
def!shell!=!new!GroovyShell(config)
76

Controlling code execution

• Your application may run user’s code
•what if the code runs in inﬁnite loops or for too long?
•what if the code consumes too many resources?

• 3 new transforms at your rescue
• @ThreadInterrupt: adds Thread#isInterrupted checks
so your executing thread stops when interrupted
• @TimedInterrupt: adds checks in method and closure bodies
to verify it’s run longer than expected
• @ConditionalInterrupt: adds checks with your own
conditional logic to break out from the user code
77

@ThreadInterrupt

@ThreadInterrupt
import%groovy.transform.ThreadInterrupt%
%
while%(true)%{

%%%%//%Any%extraterestrial%around?
}

78

@ThreadInterrupt

@ThreadInterrupt
import%groovy.transform.ThreadInterrupt%
%
while%(true)%{
{ %%%%if%(Thread.currentThread.isInterrupted())
%%%%%%%%throw$new%InterruptedException()
}
%%%%//%Any%extraterestrial%around?
}

78

@TimedInterrupt
@TimedInterrupt(10)
import!groovy.transform.TimedInterrupt!
!
while!(true)!{
!!!!move!left
!!!!//!circle!forever
}

• InterruptedException thrown
when checks indicate code ran longer than desired

79

@ConditionalInterrupt
• Specify your own condition to be inserted
at the start of method and closure bodies
• check for available resources, number of times run, etc.

• Leverages closure annotation parameters from Groovy 1.8

@ConditionalInterrupt({$battery.level$<$O.1$})
import%groovy.transform.ConditionalInterrupt

100.times%{%%%%
%%%%move%forward%at%10.km/h
}

80

Using compilation customizers

• In our previous three examples, the usage of the interrupts were explicit,
and users had to type them
• if they want to deplete the battery of your robot,
they won’t use interrupts, so you have to impose interrupts yourself

• With compilation customizers you can inject those interrupts
thanks to the ASTTransformationCustomizer

81

What have we learnt?

82

Groovy Power!™

• scripts vs classes, optional typing, colons and parens
• Groovy offers useful dynamic features for DSLs
• operator overloading, ExpandoMetaClass
• Can write almost plain natural language sentences
• for readable, concise and expressive DSLs
• Groovy DSLs are easy to integrate,
and can be secured to run safely in your own sandbox

83

Groovy Power!™ Groovy is a
great fit for
DSLs!

• scripts vs classes, optional typing, colons and parens
• Groovy offers useful dynamic features for DSLs
• operator overloading, ExpandoMetaClass
• Can write almost plain natural language sentences
• for readable, concise and expressive DSLs
• Groovy DSLs are easy to integrate,
and can be secured to run safely in your own sandbox

83

And there’s more!

• We haven’t dived into...
•How to implement your own control structures with the help of closures
•How to create Groovy « builders »
•How to hijack the Groovy syntax to develop our own language extensions with
AST Transformations
•Source preprocessing for custom syntax
•How to use the other dynamic metaprogramming techniques available
•How to improve error reporting with customizers
•IDE support with DSL descriptors (GDSL and DSLD)

84

Thank you!

ge
e Lafor lopment
Gui llaum ovy Deve
Head of Gro
om
@ gmail.c
laforge rge
Email: g @glafo o/glaforg
e
Twitter : http://gplus.t spot.com
:
G oogle+ //glaforge.app
p:
B log: htt

85

Questions & Answers

Got questions,
really?

86

Questions & Answers

I might have
answers!
Got questions,
really?

86

Image credits
• Pills: http://www.we-ew.com/wp-content/uploads/2011/01/plan-b-pills.jpg
• Chains: http://2.bp.blogspot.com/-GXDVqUYSCa0/TVdBsON4tdI/AAAAAAAAAW4/EgJOUmAxB28/s1600/breaking-chains5_copy9611.jpg
• Russian flag: http://good-wallpapers.com/pictures/4794/Russian%20Flag.jpg
• Space odissey: http://dearjesus.files.wordpress.com/2010/04/2001_a_space_odyssey_1.jpg
• HAL red: http://2.bp.blogspot.com/-yjsyPxUFicY/TcazwAltOaI/AAAAAAAAAho/GVT7wGhnrUM/s1600/2001-a-space-odyssey-HAL.jpg
• Back in time: http://4.bp.blogspot.com/-Pt44Dk9J2EM/TrQx9YNmVcI/AAAAAAAAAk4/ivWw9Lja05k/s1600/clocky.jpg
• USSR Space posters: http://www.flickr.com/photos/justinvg
• Russian General: http://rickrozoff.files.wordpress.com/2012/02/general-nikolai-makarov.jpg
• Rocket: http://blog.al.com/breaking/2009/03/soyuz_launch.jpg
• Progress capsule: http://www.spacedaily.com/images/progress-ocean-desk-1024.jpg
• Buran: http://www.buran.fr/mriya-antonov/Photos//050-Exhibition%20au%20Bourget%20avec%20Bourane-Airshow%20with%20Buran%20at%20Le%20Bourget-1134884.jpg
• Man in space: http://vintagespace.files.wordpress.com/2010/11/voskhod-2_leonov.jpg
• Sputnik 2: http://launiusr.files.wordpress.com/2010/06/sputnik2.jpg
• Lunakod: http://www.astr.ua.edu/keel/space/lunakhod_moscow.jpg
• Sandbox: http://www.turnbacktogod.com/wp-content/uploads/2008/09/sandbox.jpg
• Repair: http://www.oneangels.com/wp-content/uploads/2012/03/repair1.jpg
• Mars rover: http://wallpapers.free-review.net/wallpapers/49/Mars_rover%2C_Mars_-_03.jpg
• Mars rover 2: http://www.universetoday.com/wp-content/uploads/2011/06/551038main_pia14156-43_946-710.jpg
• Thumb: http://www.wpclipart.com/sign_language/thumbs_up_large.png.html
• Night sky: http://www.aplf-planetariums.info/galeries/ciel_profond/2004-07-01-Voie_Lactee_Scorpion-Jean-Luc_PUGLIESI.jpg
• Obama yes we can: http://www.dessinemoiunboulon.net/wp-content/uploads/2009/01/obama-yes-we-can_04-nov-08.jpg
• Hook: http://winningware.com/blog/wp-content/uploads/2009/12/FishHookXSmall.jpg
• HP 48 GX: http://calculators.torensma.net/files/images/hewlett-packard_hp-48g.jpg
• Omer: http://www.irmin.com/wallpaper/TV/Homer%20Simpson%20Oh%20No.jpg
• Cadenat: http://acsgsecurite.com/upl/site/cadenat.png

87

Going to Mars with Groovy Domain-Specific Languages

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