Implementing Groovy Domain-Specific Languages - S2G Forum - Munich 2010

Guillaume Laforge • Groovy Project Manager • JSR-241 Spec Lead • Head of Groovy Development at SpringSource / VMWare • Initiator of the Grails framework • Co-author of Groovy in Action • Speaker: JavaOne, QCon, JavaZone, Sun TechDays, Devoxx, The Spring Experience, SpringOne, JAX, Dynamic Language World, IJTC, and more... 2 lundi 22 mars 2010

Groovy in a few words ! Groovy is a dynamic language for the JVM • with a Meta Object Protocol • compiles directly to bytecode • provides seamless Java interoperability ! Groovy was created in 2003, is hosted at Codehaus, and is under the Apache license ! Relaxed grammar deriving from Java 5 • annotations, generics, static imports, enums, varargs... • borrowed good ideas from Ruby, Python, Smalltalk • flat learning curve for Java developers 3 lundi 22 mars 2010

The Context lundi 22 mars 2010

Subject Matter Expers, Business Analysts... lundi 22 mars 2010

Developer producing LOLCODE HAI CAN HAS STDIO? I HAS A VAR IM IN YR LOOP UP VAR!!1 VISIBLE VAR IZ VAR BIGGER THAN 10? KTHXBYE IM OUTTA YR LOOP KTHXBYE lundi 22 mars 2010

Lots of Languages... lundi 22 mars 2010

And in the end... nobody understands each other lundi 22 mars 2010

Expressing Requirements... 9 lundi 22 mars 2010

DSL: a potential solution? !Use a more expressive language than a general purpose one !Share a common metaphore 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 !Cleanly separate business logic from application code !Let business rules have their own lifecycle 10 lundi 22 mars 2010

Towards more readibility (1) 11 lundi 22 mars 2010

Towards more readibility (1) 20% 11 lundi 22 mars 2010

Towards more readibility (2) 12 lundi 22 mars 2010

Towards more readibility (2) 80% 12 lundi 22 mars 2010

A collection of DSLs ! In our everyday life, we’re surrounded by DSLs • Technical dialects • Notations • Business languages 13 lundi 22 mars 2010

Technical dialects 14 lundi 22 mars 2010

SQL lundi 22 mars 2010

^[w-.]+@([w-]){2,4}$ 16 lundi 22 mars 2010

Notations 17 lundi 22 mars 2010

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 lundi 22 mars 2010

L2 U F-1 B L2 F B -1 U L2 lundi 22 mars 2010

Visual! lundi 22 mars 2010

Real-life Groovy examples ! Anti-malaria drug resistance simulation ! Human Resources employee skills representation ! Insurance policies risk calculation engine ! Loan acceptance rules engine for a financial platform ! Mathematica-like lingua for nuclear safety simulations ! Market data feeds evolution scenarios ! and more... 21 lundi 22 mars 2010

Three levels of techniques Flexible & Meta- malleable syntax programming AST transformations • scripts • POGO • optional typing • categories • AST traversal • native syntax • builders • local transformations constructs • custom MetaClass • global transformations • parens / semi • ExpandoMetaClass • hooks into Antlr ommission • named arguments • BigDecimal • operator overloading • closures 22 lundi 22 mars 2010

A flexible & malleable syntax ! No need to write full-blown classes, use scripts ! Optional typing (def) • in scripts, you can even omit the def keyword ! Native syntax constructs ! Parentheses & semi-colons are optional ! Named arguments ! BigDecimal by default for decimal numbers ! Closures for custom control structures ! Operator overloading 23 lundi 22 mars 2010

Scripts vs classes ! Hide all the boilerplate technical code • an end-user doesn’t need to know about classes public class Rule { ) { public static void main(String[] args System.out.println(“Hello”); } } println “Hello” 24 lundi 22 mars 2010

Optional typing ! No need to bother with types or even generics • unless you want to! ! Imagine an interest rate lookup table method returning some generified type: Rate <LoanType, Duration, BigDecimal>[] lookupTable() { ... } def table = lookupTable() ! No need to repeat the horrible generics type info! 25 lundi 22 mars 2010

Native syntax constructs ! Lists [Monday, Tuesday, Wednesday] ! Maps [CA: ‘California’, TX: ‘Texas’] ! Ranges • You can create your own custom ranges def bizDays = Monday..Friday def allowedAge = 18..65 26 lundi 22 mars 2010

Optional parens & semis ! Make statements and expressions look more like natural languages move(left); move left 27 lundi 22 mars 2010

Named arguments ! In Groovy you can mix named and unnamed arguments for method parameters • named params are actually put in a map parameter • plus optional parens & semis take 1.pill, of: Chloroquinine, after: 6.hours ! Corresponds to a method signature like: def t ake(Map m, MedicineQuantity mq) 28 lundi 22 mars 2010

BigDecimal by default ! Main reason why financial institutions often decide to use Groovy for their business rules! • Although these days rounding issues are overrated! ! Java vs Groovy for a simple interpolation equation BigDecimal uMinusv = c.subtract(a); BigDecimal vMinusl = b.subtract(c); BigDecimal uMinusl = a.subtract(b); return e.multiply(uMinusv) .add(d.multiply(vMinusl)) _HALF_UP); .divide(uMinusl, 10, BigDecimal.ROUND (d * (b - c) + e * (c - a)) / (a - b) 29 lundi 22 mars 2010

Custom control structures, thanks to closures ! When closures are last, they can be put “out” of the parentheses surrounding parameters unless (a ccount.balance > 100.euros, { account.debit 100.euros }) unless (a ccount.balance > 100.euros) { account.debit 100.euros } ! Signature de f unless(boolean b, Closure c) 30 lundi 22 mars 2010

Operator overloading a + b a.plus(b) • Currency amounts a - b a.minus(b) 15.euros + 10.dollars a * b a.multiply(b) a / b a.divide(b) • Distance handling a % b a.modulo(b) a ** b a.power(b) 10.kilometers - 10.meters 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 -a a.unaryMinus() account += 10.dollars ~a a.bitwiseNegate() account.credit 10.dollars 31 lundi 22 mars 2010

The MOP (Meta-Object Protocol) lundi 22 mars 2010

Groovy’s MOP ! All the accesses to methods, properties, constructors, operators, etc. can be intercepted thanks to the MOP ! While Java’s behavior is hard-wired at compile-time in the class ! Groovy’s runtime behavior is adaptable at runtime through the metaclass ! Different hooks for changing the runtime behavior • GroovyObject, custom MetaClass implementation, categories, ExpandoMetaClass 33 lundi 22 mars 2010

GroovyObject ! All instances of classes created in Groovy implement the GroovyObject interface: get/setProperty(String name) invokeMeth od(String name, Object[] params) propertyMissing(String name) methodMissing( String name, Object[] params) get/setMetaClass(MetaClass mc) ! A GO can have “pretended” methods and properties 34 lundi 22 mars 2010

MetaClass ! The core of Groovy’s MOP system invokeConstructor() invokeMe thod() and invokeStaticMethod() invokeMissingMethod() getProperty() and setProperty() ge tAttribute() and setAttribute() respondsTo() and hasProperty() ! MetaClasses can change the behavior of existing third-party classes — even from the JDK 35 lundi 22 mars 2010

ExpandoMetaClass ! A DSL for MetaClasses! MoneyAmount.meta Class.constructor = { ... } Numb er.metaClass.getDollars = { ... } Di stance.metaClass.toMeters = { ... } Distance .metaClass.static.create = { ... } ! To avoid repetition of Type.metaClass, you can pass a closure to metaClass { ... } ! The delegate variable in closure represents the current instance, and it the default parameter 36 lundi 22 mars 2010

The Builder pattern lundi 22 mars 2010

A builder for HR softskills { ideas { capture 2 formulate 3 } ... } knowhow { languages { java 4 groovy 5 } ... } 38 lundi 22 mars 2010

Builders ! Builders are... • a mechanism for creating any tree-structered graph • the realization of the GoF builder pattern at the syntax level in Groovy • simply a clever use of chained method invocation, closures, parentheses omission, and use of the GroovyObject methods ! Existing builders • XML, Object graph, Swing, Ant, JMX, and more... 39 lundi 22 mars 2010

The clever trick ! GroovyObject#invokeMethod() is used to catch all non-existing method calls in the context of the builder ! The nesting of closures visually shows the level of nesting / depth in the tree ! builder.m1(attr1:1, attr2:2, { builder.m2(..., {...}) } becomes equivalent to builder.m1(attr1:1, attr2:2) { m2(...) {...} } thanks to parens omission 40 lundi 22 mars 2010

Adding properties to numbers ! Three possible approaches • create a Category • a category is a kind of decorator for default MCs • create a custom MetaClass • a full-blown MC class to implement and to set on the POGO instance • use ExpandoMetaClass • friendlier DSL approach but with a catch 41 lundi 22 mars 2010

With a Category class DistanceCategory { static Di stance getMeters(Integer self) { new Distance(self, Unit.METERS) } } use(DistanceCategory) { 100.meters } ! Interesting scope: thread-bound & lexical ! Have to surround with “use” • but there are ways to hide it 42 lundi 22 mars 2010

With an ExpandoMetaClass Number.metaClass.getMeters = {-> new Distance(delegate, Unit.METERS) } 100.meters ! Works for the class hierarchy for POJOs, and a flag exists to make it work for POGOs too ! But the catch is it’s really a global change, so beware EMC enhancements collisions 43 lundi 22 mars 2010

Compile-time Metaprogramming ! Groovy 1.6 introduced AST Transformations ! Compile-time == No runtime performance penalty! Transformation 44 lundi 22 mars 2010

Compile-time metaprogramming ! With metaprogramming, Groovy’s able to modify the behaviour of programs... at runtime ! Groovy 1.6 introduced AST Transformations • AST: Abstract Syntax Tree • Ability to change what’s being compiled at compile-time! • No runtime impact! • Lets you change the semantics of your programs! • Nice way of implementing patterns and removing boiler-plate technical code ! Two kinds of transformations: global and local 45 lundi 22 mars 2010

AST Transformations ! Two kinds of transformations • Global transformations • applicable to all compilation units • Local transformations • applicable to marked program elements • using specific marker annotations 46 lundi 22 mars 2010

AST Transformations in Groovy 1.6 ! Several (local) transformations finds their way • @Singleton — okay, not really a pattern :-) • @Immutable, @Lazy, @Delegate •@Newify • @Category and @Mixin •@PackageScope • Swing’s @Bindable and @Vetoable • Grape’s @Grab ! Let’s have a look at some of them 47 lundi 22 mars 2010

The @Singleton anti-pattern !The evil Java singleton public class Evil { ; public st atic final Evil instance = new Evil() privavte Evil() {} ; } Evil getInstance() { return instance } !In Groovy now: @Singleton class Evil {} !A lazy version also: @Singleton(lazy = true) class Evil {} 48 lundi 22 mars 2010

@Immutable ! To properly implement immutable classes • No mutators (state musn’t change) • Private final fields • Defensive copying of mutable components • Proper equals() / hashCode() / toString() for comparisons, or for keys in maps, etc. @Immutable class Coordinates { Double lat, lng } def c1 = new Coordinates(lat: 48.8, lng: 2.5) def c2 = new Coordinates(48.8, 2.5) assert c1 == c2 49 lundi 22 mars 2010

@Lazy, not just for lazy dudes! ! When you need to lazily evaluate or instantiate complex data structures for class fields, mark them with the @Lazy annotation class Dude { @Lazy pets = retrieveFromSlowDB() } ! Groovy will handle the boiler-plate code for you! 50 lundi 22 mars 2010

@Delegate Not just for managers! !You can delegate to fields of your class •Think multiple inheritance class Employee { def doTheWork() { "done" } } class Manager { ee() @Delegate Employee slave = new Employ } def god = new Manager() assert god.doTheWork() == "done" !Damn manager will get all the praise... 51 lundi 22 mars 2010

Global transformations ! Implement ASTTransformation ! Annotate the transfo specifying a compilation phase ERSION) @GroovyASTTr ansformation(phase=CompilePhase.CONV public class MyTransformation implements ASTTransformation { Unit unit) publ ic void visit(ASTNode[] nodes, Source { ... } } ! For discovery, create the file META-INF/services/ org.codehaus.groovy.transform.ASTTransformation ! Add the fully qualified name of the class in that file 52 lundi 22 mars 2010

Local transformations ! Same approach as Globale transformations ! But you don’t need the META-INF file ! Instead create an annotation to specify on which element the transformation should apply @Ret ention(RetentionPolicy.SOURCE) @Target([ElementType.METHOD]) @GroovyASTTransformationClass( ["fqn.MyTransformation"]) publ ic @interface WithLogging {...} 53 lundi 22 mars 2010

Example: the Spock framework ! Changing the semantics of the original code ! But keeping a valid Groovy syntax @Speck class HelloSpock { () { def "can you figure out what I'm up to?" expect: name.size() == size where: name << ["Kirk", "Spock", "Scotty"] size << [4, 5, 6] } } ! Check out http://www.spockframework.org 54 lundi 22 mars 2010

Various integration mechanisms ! Java 6’s javax.script.* APIs (aka JSR-223) ! Spring’s language namespace ! Groovy’s own mechanisms ! But a key idea is to externalize those DSL programs • DSL programs can have their own lifecycle • no need to redeploy an application because of a rule change • business people won’t see the technical code 55 lundi 22 mars 2010

Java 6’s javax.script.* API ! Groovy 1.6 provides its own implementation of the javax.script.* API ScriptEngineManager mgr = new ScriptEngineManager(); ScriptEngine engine = mgr.getEngineByName(“Groovy”); String result = (String)engine.eval(“2+3”); 56 lundi 22 mars 2010

Spring’s lang namespace ! POGOs (Plain Old Groovy Objects) can be pre-compiled as any POJO and used interchangeably with POJOs in a Spring application ! But Groovy scripts & classes can be loaded at runtime through the <lang:groovy/> namespace and tag ! Reloadable on change ! Customizable through a custom MetaClass <lang:groovy id="events" ovy" script-s ource="classpath:dsl/eventsChart.gro customizer-ref="eventsMetaClass" /> 57 lundi 22 mars 2010

Groovy’s own mechanisms ! Eval • for evaluating simple expressions ! GroovyShell • for more complex scripts and DSLs ! GroovyClassLoader • the most powerful mechanism 58 lundi 22 mars 2010

Eval ! Simple mechanism to evaluate math-like formulas Eval.me ( ‘3*4’) Eval.x (1, ‘3*x + 4’) Eval.xy (1, 2, ‘x + y’) Eval.xyz(1, 2, 3, ‘x * y - z’) 59 lundi 22 mars 2010

GroovyShell ! A Binding provides a context of execution • can implement lazy evaluation if needed ! A base script class can be specified def binding = new Binding() binding.mass = 22.3 binding.velocity = 10.6 def shell = new GroovyShell(binding) shell. evaluate(“mass * velocity ** 2 / 2”) 60 lundi 22 mars 2010

GroovyClassLoader ! Most powerful mechanism • could also visit or change the AST • scripts & classes can be loaded from elsewhere • more control on compilation GroovyClassLoader gcl = new GroovyClassLoader(); Class clazz = gcl.parseClass( new File(“f.groovy”)); GroovyObject instance = (GroovyObject)clazz.newInstance(); instance.setMetaClass(customMC); 61 lundi 22 mars 2010

Externalize business rules ! Although Groovy DSLs can be embedded in normal Groovy classes, you should externalize them ! Store them elsewhere • in a database, an XML file, etc. ! Benefits • Business rules are not entangled in technical application code • Business rules can have their own lifecycle, without requiring application redeployments 62 lundi 22 mars 2010

A few considerations 63 lundi 22 mars 2010

Start small, with key concepts Beware over-engineering! lundi 22 mars 2010

Grow your language progressively lundi 22 mars 2010

Get your hands dirty Play with the end-users lundi 22 mars 2010

Let your DSL fly, it’s not yours, it’s theirs! lundi 22 mars 2010

Tight feedback loop Iterative process lundi 22 mars 2010

Stay humble, You can’t get it right the 1st time. Don’t design alone at your desk Involve the end users from the start lundi 22 mars 2010

Playing it safe in a sandbox lundi 22 mars 2010

Various levels of sandboxing ! Groovy supports the usual Java Security Managers ! Use metaprogramming tricks to prevent calling / instanciating certain classes ! Create a special GroovyClassLoader AST code visitor to filter only the nodes of the AST you want to keep • ArithmeticShell in Groovy’s samples 71 lundi 22 mars 2010

Test, test, test! ! Don’t just test for nominal cases • Explicitely test for errors! ! Ensure end-users get meaninful error messages 72 lundi 22 mars 2010

Question & Answers 73 lundi 22 mars 2010

Picture credits http://www.flickr.com/photos/featheredtar/2305070061/ http://commons.wikimedia.org/wiki/File:Platypus.jpg http://www.thedailygreen.com/cm/thedailygreen/images/WT/christmas- http://www.flickr.com/photos/joaomoura/2317171808/sizes/l/ tree-with-gifts-flipbook.jpg http://www.flickr.com/photos/wiccked/132687067/ http://www.flickr.com/photos/chicoer2001/188468490/ http://www.flickr.com/photos/timsamoff/252370986/sizes/l/ http://www.flickr.com/photos/olibac/4054644737/ http://www.flickr.com/photos/29738009@N08/2975466425/sizes/l/ http://www.flickr.com/photos/epsos/3384297473/ http://www.flickr.com/photos/howie_berlin/180121635/sizes/o/ http://media.techeblog.com/images/clapboard.jpg (clap) http://www.flickr.com/photos/yogi/1281980605/sizes/l/ http://www.flickr.com/photos/diegocupolo/3614879332/ (flower power) http://www.flickr.com/photos/dorseygraphics/1336468896/sizes/l/ http://www.flickr.com/photos/oskay/237442629/sizes/m/ (danger) http://www.flickr.com/photos/xcbiker/386876546/sizes/l/ http://www.partybox.co.uk/data/partyimages/ http://www.flickr.com/photos/pietel/152403711/sizes/o/ 250x250/6ftcutoutaustinpowers.jpg (austin powers) http://www.flickr.com/photos/forezt/192554677/sizes/o/ http://www.flickr.com/photos/27663074@N07/3413698337/ (jeepers creepers) http://keremkosaner.files.wordpress.com/2008/04/softwaredevelopment.gif http://www.flickr.com/photos/wheatfields/420088151/sizes/l/ http://www.jouy.inra.fr http://www.flickr.com/photos/therefromhere/518053737/sizes/l/ http://www.flickr.com/photos/ejpphoto/408101818/sizes/o/ http://www.flickr.com/photos/romainguy/230416692/sizes/l/ http://www.flickr.com/photos/solaro/2127576608/sizes/l/ http://www.flickr.com/photos/addictive_picasso/2874279971/sizes/l/ http://www.flickr.com/photos/biggreymare/2846899405/sizes/l/ http://www.flickr.com/photos/huangjiahui/3127634297/sizes/l/ http://www.flickr.com/photos/wwworks/2222523978/ (earth) http://www.flickr.com/photos/25831000@N08/3064515804/sizes/o/ http://static-p3.fotolia.com/jpg/ 00/01/64/30/400_F_1643044_YrBQoPnt0SC5gHAueG0bhx20yCSL42.jpg (trafic light) http://www.flickr.com/photos/lanier67/3147696168/sizes/l/ http://aldaria02.a.l.pic.centerblog.net/lz2levrz.jpg (griffon) http://www.flickr.com/photos/ktb/4916063/sizes/o/ http://www.flickr.com/photos/geishaboy500/104137788/ (soap) http://www.flickr.com/photos/nathonline/918128338/sizes/l/ Matriochka http://lang.russe.free.fr/images/matriochka.jpg http://www.flickr.com/photos/kevinsteele/39300193/sizes/l/ http://commons.wikimedia.org/wiki/File:Brueghel-tower-of-babel.jpg 74 lundi 22 mars 2010

Implementing Groovy Domain-Specific Languages - S2G Forum - Munich 2010

by Guillaume Laforge

Accessibility

Upload Details

Usage Rights

1 Embed 7

Statistics

Implementing Groovy Domain-Specific Languages - S2G Forum - Munich 2010 Presentation Transcript