Design Your Own Domain-Specific Language
    with Groovy!
    Guillaume Laforge
    Groovy Project Manager




           ...
Guillaume Laforge

    • Groovy Project Manager
    • JSR-241 Spec Lead

    • Head of Groovy Development
      at SpringS...
Groovy in a few words


    ! Groovy is a dynamic language for the JVM
       • with a Meta Object Protocol
       • compi...
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
     ...
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 metaph...
Towards more readibility (1)




                                   11

lundi 22 mars 2010
Towards more readibility (1)




                                   11

lundi 22 mars 2010
Towards more readibility (1)




                                   20%




                                         11

l...
Towards more readibility (2)




                                   12

lundi 22 mars 2010
Towards more readibility (2)




                                   12

lundi 22 mars 2010
Towards more readibility (2)




                                   80%



                                         12

lu...
A collection of DSLs


    ! In our everyday life, we’re surrounded by DSLs

       • Technical dialects
       • Notation...
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 representa...
Three levels of techniques




   Flexible &               Meta-
   malleable syntax         programming          AST
    ...
A flexible & malleable syntax


    ! No need to write full-blown classes, use scripts
    ! Optional typing (def)
       ...
Scripts vs classes



      ! Hide all the boilerplate technical code
         • an end-user doesn’t need to know about cl...
Optional typing



      ! No need to bother with types or even generics
         • unless you want to!

      ! Imagine a...
Native syntax constructs
    ! Lists
                        [Monday, Tuesday, Wednesday]

    ! Maps
                    ...
Optional parens & semis
    ! Make statements and expressions
       look more like natural languages




                ...
Named arguments
    ! In Groovy you can mix named and unnamed arguments for method
       parameters
       • named params...
BigDecimal by default



    ! Main reason why financial institutions often decide to use Groovy for
       their business...
Custom control structures,
    thanks to closures
    ! When closures are last, they can be put “out” of the parentheses
 ...
Operator overloading


    a + b            a.plus(b)
                                         • Currency amounts
    a - ...
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 ...
GroovyObject



      ! All instances of classes created in Groovy implement the
         GroovyObject interface:

       ...
MetaClass
    ! The core of Groovy’s MOP system

                     invokeConstructor()
                     invokeMe th...
ExpandoMetaClass
    ! A DSL for MetaClasses!

                MoneyAmount.meta Class.constructor = { ... }
              ...
The Builder pattern



lundi 22 mars 2010
A builder for HR



       softskills {
           ideas {
                capture 2
                formulate 3
         ...
A builder for HR



       softskills {
           ideas {
                capture 2
                formulate 3
         ...
Builders



! Builders are...
   • a mechanism for creating any tree-structered graph
   • the realization of the GoF buil...
The clever trick
    ! GroovyObject#invokeMethod() is used to catch all non-existing
      method calls in the context of ...
Adding properties to numbers
    ! Three possible approaches

       • create a Category
          • a category is a kind ...
With a Category



               class DistanceCategory {
                   static Di stance getMeters(Integer self) {
 ...
With an ExpandoMetaClass



               Number.metaClass.getMeters = {->
                   new Distance(delegate, Unit...
Compile-time Metaprogramming


    ! Groovy 1.6 introduced AST Transformations

    ! Compile-time == No runtime performan...
Compile-time metaprogramming
    ! With metaprogramming, Groovy’s able to modify the behaviour of
       programs... at ru...
AST Transformations
    ! Two kinds of transformations

       • Global transformations
          • applicable to all comp...
AST Transformations
    in Groovy 1.6
    ! Several (local) transformations finds their way
       • @Singleton — okay, no...
The @Singleton anti-pattern


    !The evil Java singleton

                     public class Evil {                      ...
@Immutable
    ! To properly implement immutable classes
       • No mutators (state musn’t change)
       • Private final...
@Lazy, not just for lazy dudes!
    ! When you need to lazily evaluate or instantiate complex data
       structures for c...
@Delegate
    Not just for managers!
    !You can delegate to fields of your class
       •Think multiple inheritance

   ...
Global transformations
    ! Implement ASTTransformation
    ! Annotate the transfo specifying a compilation phase

      ...
Local transformations
    ! Same approach as Globale transformations
    ! But you don’t need the META-INF file
    ! Inst...
Example: the Spock framework
    ! Changing the semantics of the original code
    ! But keeping a valid Groovy syntax

  ...
Various integration mechanisms
    ! Java 6’s javax.script.* APIs (aka JSR-223)
    ! Spring’s language namespace
    ! Gr...
Java 6’s javax.script.* API



      ! Groovy 1.6 provides its own implementation of the javax.script.* API



           ...
Spring’s lang namespace



      ! POGOs (Plain Old Groovy Objects) can be pre-compiled as any
        POJO and used inter...
Groovy’s own mechanisms
    ! Eval
       • for evaluating simple expressions

    ! GroovyShell
       • for more complex...
Eval



      ! Simple mechanism to evaluate math-like formulas




                     Eval.me (           ‘3*4’)
      ...
GroovyShell



      ! A Binding provides a context of execution
         • can implement lazy evaluation if needed



   ...
GroovyClassLoader



      ! Most powerful mechanism
         • could also visit or change the AST
         • scripts & cl...
Externalize business rules
    ! Although Groovy DSLs can be embedded in normal Groovy classes,
       you should external...
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 f...
Playing it safe in a sandbox
lundi 22 mars 2010
Various levels
    of sandboxing




    ! Groovy supports the usual
       Java Security Managers

    ! Use metaprogramm...
Test, test, test!


    ! Don’t just test for nominal cases
       • Explicitely test for errors!

    ! Ensure end-users ...
Question & Answers




                         73

lundi 22 mars 2010
Picture credits


         http://www.flickr.com/photos/featheredtar/2305070061/                 http://commons.wikimedia....
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Implementing Groovy Domain-Specific Languages - S2G Forum - Munich 2010

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

  1. 1. Design Your Own Domain-Specific Language with Groovy! Guillaume Laforge Groovy Project Manager © 2010 SpringSource, A division of VMware. All rights reserved lundi 22 mars 2010
  2. 2. 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
  3. 3. 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
  4. 4. The Context lundi 22 mars 2010
  5. 5. Subject Matter Expers, Business Analysts... lundi 22 mars 2010
  6. 6. 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
  7. 7. Lots of Languages... lundi 22 mars 2010
  8. 8. And in the end... nobody understands each other lundi 22 mars 2010
  9. 9. Expressing Requirements... 9 lundi 22 mars 2010
  10. 10. 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
  11. 11. Towards more readibility (1) 11 lundi 22 mars 2010
  12. 12. Towards more readibility (1) 11 lundi 22 mars 2010
  13. 13. Towards more readibility (1) 20% 11 lundi 22 mars 2010
  14. 14. Towards more readibility (2) 12 lundi 22 mars 2010
  15. 15. Towards more readibility (2) 12 lundi 22 mars 2010
  16. 16. Towards more readibility (2) 80% 12 lundi 22 mars 2010
  17. 17. A collection of DSLs ! In our everyday life, we’re surrounded by DSLs • Technical dialects • Notations • Business languages 13 lundi 22 mars 2010
  18. 18. Technical dialects 14 lundi 22 mars 2010
  19. 19. SQL lundi 22 mars 2010
  20. 20. ^[w-.]+@([w-]){2,4}$ 16 lundi 22 mars 2010
  21. 21. Notations 17 lundi 22 mars 2010
  22. 22. 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 lundi 22 mars 2010
  23. 23. L2 U F-1 B L2 F B -1 U L2 lundi 22 mars 2010
  24. 24. Visual! lundi 22 mars 2010
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. 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
  30. 30. 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
  31. 31. Optional parens & semis ! Make statements and expressions look more like natural languages move(left); move left 27 lundi 22 mars 2010
  32. 32. 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
  33. 33. 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
  34. 34. 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
  35. 35. 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
  36. 36. The MOP (Meta-Object Protocol) lundi 22 mars 2010
  37. 37. 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
  38. 38. 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
  39. 39. 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
  40. 40. 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
  41. 41. The Builder pattern lundi 22 mars 2010
  42. 42. A builder for HR softskills { ideas { capture 2 formulate 3 } ... } knowhow { languages { java 4 groovy 5 } ... } 38 lundi 22 mars 2010
  43. 43. A builder for HR softskills { ideas { capture 2 formulate 3 } ... } knowhow { languages { java 4 groovy 5 } ... } 38 lundi 22 mars 2010
  44. 44. 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
  45. 45. 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
  46. 46. 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
  47. 47. 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
  48. 48. 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
  49. 49. Compile-time Metaprogramming ! Groovy 1.6 introduced AST Transformations ! Compile-time == No runtime performance penalty! Transformation 44 lundi 22 mars 2010
  50. 50. 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
  51. 51. 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
  52. 52. 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
  53. 53. 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
  54. 54. @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
  55. 55. @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
  56. 56. @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
  57. 57. 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
  58. 58. 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
  59. 59. 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
  60. 60. 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
  61. 61. 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
  62. 62. 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
  63. 63. 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
  64. 64. 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
  65. 65. 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
  66. 66. 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
  67. 67. 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
  68. 68. A few considerations 63 lundi 22 mars 2010
  69. 69. Start small, with key concepts Beware over-engineering! lundi 22 mars 2010
  70. 70. Grow your language progressively lundi 22 mars 2010
  71. 71. Get your hands dirty Play with the end-users lundi 22 mars 2010
  72. 72. Let your DSL fly, it’s not yours, it’s theirs! lundi 22 mars 2010
  73. 73. Tight feedback loop Iterative process lundi 22 mars 2010
  74. 74. 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
  75. 75. Playing it safe in a sandbox lundi 22 mars 2010
  76. 76. 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
  77. 77. 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
  78. 78. Question & Answers 73 lundi 22 mars 2010
  79. 79. 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

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