groovy rules

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Dr Paul King

@paulk_asert

http:/slideshare.net/paulk_asert/groovy-rules

https://github.com/paulk-asert/groovy-rules

Leveraging Groovy for

Capturing Business Rules

Topics

Introduction to DSLs

• Introduction to Groovy

• DSLs in Groovy

• Why Groovy?

• Tortoise & Crane Example

• Einstein’s Riddle

• Further Discussion

• More Info

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What is a DSL?

• 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

– declarative data << DSL << general-purpose programming

language (GPL)

– AKA: fluent / human interfaces, language oriented

programming, problem-oriented languages, little / mini

languages, macros, business natural languages Sources:

http://en.wikipedia.org/wiki/Domain-specific_language

van Deursen, A., Klint, P., Visser, J.: Domain-specific languages: an annotated bibliography. ACM SIGPLAN Notices 35 (2000) 26–36

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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

boilerplate technical code thanks to a

clean separation

• Let business rules have their own lifecycle

Why Scripting DSLs package org.drools.examples.golfing; dialect "mvel" import org.drools.examples.golfing.GolfingExample.Golfer; rule "find solution" when // Bob is wearing plaid pants

$bob : Golfer( name == "Bob", color == "plaid") // ... then

System.out.println( "Bob " + $bob.getColor() ); end

package org.drools.examples.golfing; dialect "mvel" import org.drools.examples.golfing.GolfingExample.Golfer; rule "find solution" when

Bob is wearing plaid pants // ... then

Display all details end

when Bob is wearing plaid pants display all details

Compile time

translation

Compile time

or runtime

translation

Why a DSL?

• Advantages:

– Domain experts can

understand, validate,

modify, and often even

develop DSL programs

– Self-documenting (?)

– Enhance quality,

productivity, reliability,

maintainability, portability

and reusability

– Safety; language

constructs can be made

safe

– Tooling

• Disadvantages:

– Learning cost vs. limited

applicability

– Cost of designing,

implementing &

maintaining DSL & tools

– Attaining proper scope

– Trade-offs between DSL

specific and general-

purpose programming

language constructs

– Efficiency costs

– Proliferation of similar

non-standard DSLs

– Tooling

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Topics

• Introduction to DSLs

Introduction to Groovy

• DSLs in Groovy

• Why Groovy?




• More Info

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Java code for list manipulation

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import java.util.List; import java.util.ArrayList; class Main { private List keepShorterThan(List strings, int length) { List result = new ArrayList(); for (int i = 0; i < strings.size(); i++) { String s = (String) strings.get(i); if (s.length() < length) { result.add(s); } } return result; } public static void main(String[] args) { List names = new ArrayList(); names.add("Ted"); names.add("Fred"); names.add("Jed"); names.add("Ned"); System.out.println(names); Main main = new Main(); List shortNames = main.keepShorterThan(names, 4); System.out.println(shortNames.size()); for (int i = 0; i < shortNames.size(); i++) { String s = (String) shortNames.get(i); System.out.println(s); } } }

Based on an

example by

Jim Weirich

& Ted Leung

Groovy code for list manipulation

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Rename

Main.java

to Main.groovy

Some Java Boilerplate identified

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Are the semicolons

needed?

And shouldn’t

we us more

modern list

notation?

Why not

import common

libraries?

Do we need

the static types?

Must we always

have a main

method and

class definition?

How about

improved

consistency?

Java Boilerplate removed

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def keepShorterThan(strings, length) { def result = new ArrayList() for (s in strings) { if (s.size() < length) { result.add(s) } } return result } names = new ArrayList() names.add("Ted"); names.add("Fred") names.add("Jed"); names.add("Ned") System.out.println(names) shortNames = keepShorterThan(names, 4) System.out.println(shortNames.size()) for (s in shortNames) { System.out.println(s) }

More Java Boilerplate identified

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def keepShorterThan(strings, length) { def result = new ArrayList() for (s in strings) { if (s.size() < length) { result.add(s) } } return result } names = new ArrayList() names.add("Ted"); names.add("Fred") names.add("Jed"); names.add("Ned") System.out.println(names) shortNames = keepShorterThan(names, 4) System.out.println(shortNames.size()) for (s in shortNames) { System.out.println(s) }

Shouldn’t we

have special

notation for lists?

And special

facilities for

list processing?

Is ‘return’

needed at end?

Is the method

now needed?

Simplify common

methods?

Remove unambiguous

brackets?

Boilerplate removed = nicer Groovy version

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names = ["Ted", "Fred", "Jed", "Ned"] println names shortNames = names.findAll{ it.size() < 4 } println shortNames.size() shortNames.each{ println it }

["Ted", "Fred", "Jed", "Ned"] 3 Ted Jed Ned

Output:

Or Groovy DSL version if required

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names = [] def of, having, less = null def given(_the) { [names:{ Object[] ns -> names.addAll(ns) [and: { n -> names += n }] }] } def the = [ number: { _of -> [names: { _having -> [size: { _less -> [than: { size -> println names.findAll{ it.size() < size }.size() }]}] }] }, names: { _having -> [size: { _less -> [than: { size -> names.findAll{ it.size() < size }.each{ println it } }]}] } ] def all = [ the: { println names } ] def display(arg) { arg }

given the names "Ted", "Fred", "Jed" and "Ned" display all the names display the number of names having size less than 4 display the names having size less than 4

Closures

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int twice(int arg) { arg * 2 } def triple = { int arg -> arg * 3 } println twice(3) // => 6 println triple(3) // => 9

Grapes / Grab: Google collections

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@Grab('com.google.guava:guava:r09') import com.google.common.collect.HashBiMap HashBiMap fruit = [grape:'purple', lemon:'yellow', lime:'green'] assert fruit.lemon == 'yellow' assert fruit.inverse().yellow == 'lemon'

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Groovy Builders

<html> <head> <title>Hello</title> </head> <body> <ul> <li>world 1</li> <li>world 2</li> <li>world 3</li> <li>world 4</li> <li>world 5</li> </ul> </body> </html>

import groovy.xml.* def page = new MarkupBuilder() page.html { head { title 'Hello' } body { ul { for (count in 1..5) { li "world $count" } } } }

• Markup Builder

Topics



DSLs in Groovy

• Why Groovy?




• More Info

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DSL example...

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class FluentApi { def action, what def the(what) { this.what = what; this } def of(arg) { action(what(arg)) } } show = { arg -> println arg } square_root = { Math.sqrt(it) } please = { new FluentApi(action: it) } please show the square_root of 100 // => 10.0

…DSL example...

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DSL implementation details

…DSL example...

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DSL usage

…DSL example...

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please show the square_root of 100

…DSL example...

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please show the square_root of 100

please(show).the(square_root).of(100)

…DSL example...

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class FluentApi { def action, what def the(what) { this.what = what; this } def of(arg) { action(what(arg)) } } show = { arg -> println arg } square_root = { Math.sqrt(it) } please = { new FluentApi(action: it) } please(show).the(square_root).of(100)

…DSL example...

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Object.metaClass.please = { clos -> clos(delegate) } Object.metaClass.the = { clos -> delegate[1](clos(delegate[0])) } show = { thing -> [thing, { println it }] } square_root = { Math.sqrt(it) } given = { it } given 100 please show the square_root // ==> 10.0

...DSL example...

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show = { println it } square_root = { Math.sqrt(it) } def please(action) { [the: { what -> [of: { n -> action(what(n)) }] }] } please show the square_root of 100 // ==> 10.0

...DSL example...

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show = { println it } square_root = { Math.sqrt(it) } def please(action) { [the: { what -> [of: { n -> action(what(n)) }] }] } please show the square_root of 100 // ==> 10.0

Inspiration for this example came from …

...DSL example

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// Japanese DSL using GEP3 rules Object.metaClass.を = Object.metaClass.の = { clos -> clos(delegate) } まず = { it } 表示する = { println it } 平方根 = { Math.sqrt(it) } まず 100 の平方根を表示する // First, show the square root of 100 // => 10.0

source: http://d.hatena.ne.jp/uehaj/20100919/1284906117

also: http://groovyconsole.appspot.com/edit/241001

Topics



• DSLs in Groovy

Why Groovy?




• More Info

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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,

app’n server apps – compile into bytecode or leave in source form

– also security and safety

Compile-time Metaprogramming

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Transformation

@Immutable...

• Java Immutable Class – As per Joshua Bloch

Effective Java

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public final class Person { private final String first; private final String last; public String getFirst() { return first; } public String getLast() { return last; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((first == null) ? 0 : first.hashCode()); result = prime * result + ((last == null) ? 0 : last.hashCode()); return result; } public Person(String first, String last) { this.first = first; this.last = last; } // ...

// ... @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (first == null) { if (other.first != null) return false; } else if (!first.equals(other.first)) return false; if (last == null) { if (other.last != null) return false; } else if (!last.equals(other.last)) return false; return true; } @Override public String toString() { return "Person(first:" + first + ", last:" + last + ")"; } }

...@Immutable...

• Java Immutable Class – As per Joshua Bloch

Effective Java

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public final class Person { private final String first; private final String last; public String getFirst() { return first; } public String getLast() { return last; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((first == null) ? 0 : first.hashCode()); result = prime * result + ((last == null) ? 0 : last.hashCode()); return result; } public Person(String first, String last) { this.first = first; this.last = last; } // ...

// ... @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (first == null) { if (other.first != null) return false; } else if (!first.equals(other.first)) return false; if (last == null) { if (other.last != null) return false; } else if (!last.equals(other.last)) return false; return true; } @Override public String toString() { return "Person(first:" + first + ", last:" + last + ")"; } }

boilerplate

...@Immutable

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@Immutable class Person { String first, last }

Rules engines • Backward chaining starts with a list of goals (or a

hypothesis) and works backwards applying rules to

derive new hypotheses until available data is found

to support the hypotheses or all rules and data have

been exhausted

– http://en.wikipedia.org/wiki/Backward_chaining

• Forward chaining starts with the available facts and

applies rules to derive or infer more facts until a

goal is reached

– http://en.wikipedia.org/wiki/Forward_chaining

http://en.wikipedia.org/wiki/Backward_chaining

http://en.wikipedia.org/wiki/Forward_chaining



Backward chaining example

• Rules – If X croaks and eats flies – Then X is a frog

– If X chirps and sings – Then X is a canary

– If X is a frog – Then X is green

– If X is a canary – Then X is yellow

• Facts – Fritz croaks

– Fritz eats flies

– Tweety eats flies

– Tweety chirps

– Tweety is yellow

Who is a frog?

? is a frog

Based on rule 1, the computer can derive:

2. ? croaks and eats flies

Based on logic, the computer can derive:

3. ? croaks and ? eats flies

Based on the facts, the computer can derive:

4. Fritz croaks and Fritz eats flies

Forward chaining example

• Rules – If X croaks and eats flies – Then X is a frog

– If X chirps and sings – Then X is a canary

– If X is a frog – Then X is green

– If X is a canary – Then X is yellow

• Facts – Fritz croaks

– Fritz eats flies

– Tweety eats flies

– Tweety chirps

– Tweety is yellow

Who is a frog?

1. Fritz croaks and Fritz eats flies

Based on logic, the computer can derive:

2. Fritz croaks and eats flies

Based on rule 1, the computer can derive:

3. Fritz is a frog

Drools Expert Golfing Example… /* * Copyright 2010 JBoss Inc * Licensed under the Apache License… */ package org.drools.examples.golfing; import org.drools.KnowledgeBase; import org.drools.KnowledgeBaseFactory; import org.drools.builder.KnowledgeBuilder; import org.drools.builder.KnowledgeBuilderFactory; import org.drools.builder.ResourceType; import org.drools.io.ResourceFactory; import org.drools.runtime.StatefulKnowledgeSession; public class GolfingExample { /** * @param args */ public static void main(final String[] args) { final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); kbuilder.add(ResourceFactory.newClassPathResource("golf.drl", GolfingExample.class), ResourceType.DRL); final KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); kbase.addKnowledgePackages(kbuilder.getKnowledgePackages()); final StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession(); String[] names = new String[]{"Fred", "Joe", "Bob", "Tom"}; String[] colors = new String[]{"red", "blue", "plaid", "orange"}; int[] positions = new int[]{1, 2, 3, 4}; for (int n = 0; n < names.length; n++) { for (int c = 0; c < colors.length; c++) { for (int p = 0; p < positions.length; p++) { ksession.insert(new Golfer(names[n], colors[c], positions[p])); } } } // ...

// ... ksession.fireAllRules(); ksession.dispose(); } public static class Golfer { private String name; private String color; private int position; public Golfer() { } public Golfer(String name, String color, int position) { super(); this.name = name; this.color = color; this.position = position; } /** * @return the color */ public String getColor() { return this.color; } /** * @return the name */ public String getName() { return this.name; } /** * @return the name */ public int getPosition() { return this.position; } } }

…Drools Expert Golfing Example import groovy.transform.Immutable import static org.drools.builder.ResourceType.DRL import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newClassPathResource

def kbuilder = newKnowledgeBuilder() kbuilder.add(newClassPathResource("golf.drl", getClass()), DRL) def kbase = newKnowledgeBase() kbase.addKnowledgePackages(kbuilder.knowledgePackages) def ksession = kbase.newStatefulKnowledgeSession()

def names = ["Fred", "Joe", "Bob", "Tom"] def colors = ["red", "blue", "plaid", "orange"] def positions = [1, 2, 3, 4] [names, colors, positions].combinations().each { n, c, p -> ksession.insert(new Golfer(n, c, p)) } ksession.fireAllRules() ksession.dispose()

@Immutable class Golfer { String name String color int position }

@Grab…

• Set up dependencies as per Java – E.g. manually add to classpath or use

Maven/Gradle/Ant or rely on IDE features

• Or @Grab declares dependencies inline – Makes scripts environment independent

– Downloads transient dependencies as needed

– (Uncomment in github examples)

//@GrabResolver('https://repository.jboss.org/nexus/content/groups/public-jboss/') //@Grab('org.drools:drools-compiler:5.5.0.Final') //@Grab('org.drools:drools-core:5.5.0.Final') //@Grab('com.sun.xml.bind:jaxb-xjc:2.2.5.jboss-1;transitive=false') //@Grab('com.google.protobuf:protobuf-java:2.4.1') //@Grab('org.slf4j:slf4j-simple:1.6.4') import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newClassPathResource def kbuilder = newKnowledgeBuilder() // ...

…@Grab…

> groovy -classpath C:\Projects\GroovyProblemSolvers\out\production\DroolsExpert; C:\Users\paulk\.groovy\grapes\org.drools\drools-compiler\jars\drools-compiler-5.3.3.Final.jar; C:\Users\paulk\.groovy\grapes\org.antlr\antlr-runtime\jars\antlr-runtime-3.3.jar; C:\Users\paulk\.groovy\grapes\org.antlr\antlr\jars\antlr-3.3.jar; C:\Users\paulk\.groovy\grapes\org.antlr\stringtemplate\jars\stringtemplate-3.2.1.jar; C:\Users\paulk\.groovy\grapes\antlr\antlr\jars\antlr-2.7.7.jar; C:\Users\paulk\.groovy\grapes\org.eclipse.jdt.core.compiler\ecj\jars\ecj-3.5.1.jar; C:\Users\paulk\.groovy\grapes\org.mvel\mvel2\jars\mvel2-2.1.0.drools16.jar; C:\Users\paulk\.groovy\grapes\com.sun.xml.bind\jaxb-xjc\jars\jaxb-xjc-2.2.5.jboss-1.jar; C:\Users\paulk\.groovy\grapes\com.sun.xml.bind\jaxb-impl\jars\jaxb-impl-2.2.5.jboss-1.jar; C:\Users\paulk\.groovy\grapes\javax.xml.bind\jaxb-api\jars\jaxb-api-2.2.6.jar; C:\Users\paulk\.groovy\grapes\com.sun.istack\istack-commons-runtime\jars\istack-commons-runtime-2.6.1.jar; C:\Users\paulk\.groovy\grapes\javax.xml.stream\stax-api\jars\stax-api-1.0-2.jar; C:\Users\paulk\.groovy\grapes\javax.activation\activation\jars\activation-1.1.jar; C:\Users\paulk\.groovy\grapes\com.sun.xml.txw2\txw2\jars\txw2-20110809.jar; C:\Users\paulk\.groovy\grapes\relaxngDatatype\relaxngDatatype\jars\relaxngDatatype-20020414.jar; C:\Users\paulk\.groovy\grapes\com.sun.codemodel\codemodel\jars\codemodel-2.6.jar; C:\Users\paulk\.groovy\grapes\com.sun.xml.dtd-parser\dtd-parser\jars\dtd-parser-1.1.jboss-1.jar; C:\Users\paulk\.groovy\grapes\com.sun.istack\istack-commons-tools\jars\istack-commons-tools-2.6.1.jar; C:\Users\paulk\.groovy\grapes\org.apache.ant\ant\jars\ant-1.7.0.jar; C:\Users\paulk\.groovy\grapes\org.apache.ant\ant-launcher\jars\ant-launcher-1.7.0.jar; C:\Users\paulk\.groovy\grapes\org.kohsuke.rngom\rngom\jars\rngom-201103.jboss-1.jar; C:\Users\paulk\.groovy\grapes\com.sun.xsom\xsom\jars\xsom-20110809.jar; C:\Users\paulk\.groovy\grapes\xml-resolver\xml-resolver\jars\xml-resolver-1.1.jar; C:\Users\paulk\.groovy\grapes\org.drools\drools-core\jars\drools-core-5.3.3.Final.jar; C:\Users\paulk\.groovy\grapes\org.drools\knowledge-api\jars\knowledge-api-5.3.3.Final.jar; C:\Projects\GroovyProblemSolvers\DroolsExpert\src\resources GolfExample.groovy

Or you can precompile: > groovyc -classpath ... GolfExample.groovy > jar ... Then use groovy or java commands to run.

Old school

…@Grab…

> groovy GolfExample.groovy

@GrabResolver('https://repository.jboss.org/nexus/content/groups/public-jboss/') @Grab('org.drools:drools-compiler:5.5.0.Final') @Grab('org.drools:drools-core:5.5.0.Final') @Grab('com.sun.xml.bind:jaxb-xjc:2.2.5.jboss-1;transitive=false') @Grab('com.google.protobuf:protobuf-java:2.4.1') @Grab('org.slf4j:slf4j-simple:1.6.4') import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newClassPathResource def kbuilder = newKnowledgeBuilder() // ...

With @Grab

…@Grab

> groovy GolfExample

With @Grab

@GrabResolver('https://repository.jboss.org/nexus/content/groups/public-jboss/') @Grab('org.drools:drools-compiler:5.5.0.Final') @Grab('org.drools:drools-core:5.5.0.Final') @Grab('com.sun.xml.bind:jaxb-xjc:2.2.5.jboss-1;transitive=false') @Grab('com.google.protobuf:protobuf-java:2.4.1') @Grab('org.slf4j:slf4j-simple:1.6.4') import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newClassPathResource def kbuilder = newKnowledgeBuilder() // ...

golf.drl… dialect "mvel" import Golfer; rule "find solution" when // There is a golfer named Fred, $fred : Golfer( name == "Fred" ) // Joe is in position 2 $joe : Golfer( name == "Joe", position == 2, position != $fred.position, color != $fred.color ) // Bob is wearing plaid pants $bob : Golfer( name == "Bob", position != $fred.position, position != $joe.position, color == "plaid", color != $fred.color, color != $joe.color ) // ...

…golf.drl // Tom isn't in position 1 or 4 // and isn't wearing orange $tom : Golfer( name == "Tom", position != 1, position != 4, position != $fred.position, position != $joe.position, position != $bob.position, color != "orange", color != $fred.color, color != $joe.color, color != $bob.color ) // The golfer to Fred's immediate right // is wearing blue pants Golfer( position == ( $fred.position + 1 ), color == "blue", this in ( $joe, $bob, $tom ) ) then System.out.println("Fred " + $fred.getPosition() + " " + $fred.getColor()); System.out.println("Joe " + $joe.getPosition() + " " + $joe.getColor()); System.out.println("Bob " + $bob.getPosition() + " " + $bob.getColor()); System.out.println("Tom " + $tom.getPosition() + " " + $tom.getColor()); end

Topics



• DSLs in Groovy

• Why Groovy?

Tortoise & Crane Example



• More Info

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Tortoises & Cranes

• Around a pond dwell tortoises and cranes

• There are 7 animals in total

• There are 20 legs in total

• How many of each animal are there?

Source: http://www.youtube.com/watch?v=tUs4olWQYS4

Tortoises & Cranes: Choco… //@GrabResolver('http://www.emn.fr/z-info/choco-repo/mvn/repository') //@Grab('choco:choco-solver:2.1.5') import static choco.Choco.* import choco.cp.model.CPModel import choco.cp.solver.CPSolver

def m = new CPModel() def s = new CPSolver()

def totalAnimals = 7 def totalLegs = 20 def c = makeIntVar('Cranes', 0, totalAnimals) def t = makeIntVar('Tortoises', 0, totalAnimals) m.addConstraint(eq(plus(c, t), totalAnimals)) m.addConstraint(eq(plus(mult(c, 2), mult(t, 4)), totalLegs)) s.read(m)

def more = s.solve() while (more) { println "Found a solution:" [c, t].each { def v = s.getVar(it) if (v.val) println " $v.val * $v.name" } more = s.nextSolution() }

Found a solution:

4 * Cranes

3 * Tortoises

…Tortoises & Cranes: Choco import static choco.Choco.* import choco.cp.model.CPModel import choco.cp.solver.CPSolver import choco.kernel.model.variables.integer.IntegerVariable

def m = new CPModel() def s = new CPSolver()

def totalAnimals = 7 def totalLegs = 20 def c = makeIntVar('Cranes', 0, totalAnimals) def t = makeIntVar('Tortoises', 0, totalAnimals) IntegerVariable[] animals = [c, t] m.addConstraint(eq(plus(c, t), totalAnimals)) m.addConstraint(eq(scalar(animals, [2, 4] as int[]), totalLegs)) s.read(m)

def more = s.solve() while (more) { println "Found a solution:" animals.each { def v = s.getVar(it) if (v.val) println " $v.val * $v.name" } more = s.nextSolution() }

Slight variant

using scalars.

Well suited to

scaling to

more animals

Tortoises & Cranes: Simplistic… import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newReaderResource

def numAnimals = 7 def numLegs = 20 def kbuilder = newKnowledgeBuilder() kbuilder.add(newReaderResource(new StringReader(''' dialect "mvel" rule "deduce animal counts" when $crane : Crane( ) $tortoise : Tortoise( quantity + $crane.quantity == ''' + numAnimals + ''', quantity * numLegs + $crane.quantity * $crane.numLegs == ''' + numLegs + ''' ) then System.out.println( "Cranes " + $crane.getQuantity() ) System.out.println( "Tortoises " + $tortoise.getQuantity() ) end ''')), ResourceType.DRL) def kbase = newKnowledgeBase() kbase.addKnowledgePackages(kbuilder.knowledgePackages) def ksession = kbase.newStatefulKnowledgeSession() …

import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newReaderResource


…Tortoises & Cranes: Simplistic… … (numAnimals + 1).times { n -> if (numLegs.intdiv(Crane.numLegs) >= n) { ksession.insert(new Crane(n)) } if (numLegs.intdiv(Tortoise.numLegs) >= n) { ksession.insert(new Tortoise(n)) } } ksession.fireAllRules() ksession.dispose() @Immutable class Crane { static int numLegs = 2 int quantity } @Immutable class Tortoise { static int numLegs = 4 int quantity }

import groovy.transform.Immutable import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.newKnowledgeBase import static org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder import static org.drools.io.ResourceFactory.newReaderResource


…Tortoises & Cranes: Simplistic … (numAnimals + 1).times { n -> if (numLegs.intdiv(Crane.numLegs) >= n) { ksession.insert(new Crane(n)) } if (numLegs.intdiv(Tortoise.numLegs) >= n) { ksession.insert(new Tortoise(n)) } } ksession.fireAllRules() ksession.dispose() @Immutable class Crane { static int numLegs = 2 int quantity } @Immutable class Tortoise { static int numLegs = 4 int quantity }

What is the impact

of adding another

kind of animal?

Tortoises & Cranes: DSL… //@GrabResolver('https://repository.jboss.org/nexus/content/groups/public-jboss/') //@Grab('org.drools:knowledge-api:5.4.0.Final') //@Grab('org.drools:drools-compiler:5.4.0.Final') //@Grab('org.drools:drools-core:5.4.0.Final') //@Grab('com.sun.xml.bind:jaxb-xjc:2.2.5.jboss-1') //@GrabExclude('com.github.relaxng:relaxngDatatype')

import groovy.transform.Field import org.drools.builder.ResourceType import static org.drools.KnowledgeBaseFactory.* import static org.drools.builder.KnowledgeBuilderFactory.* import static org.drools.io.ResourceFactory.newReaderResource

class Solver { static main(Map animals, int totalAnimals, int totalLegs, ClassLoader loader) { def whenClauses = '' def thenClauses = '' def numAnimalsClause = '' def numLegsClause = '' def lastIndex = animals.size() - 1 animals.eachWithIndex { entry, index -> def key = entry.key def capKey = key.capitalize() whenClauses += ' $' + "$key : $capKey (" thenClauses += " System.out.println( \"$capKey \"" + ' + $' + key + '.getQuantity() )\n' if (index != lastIndex) { numAnimalsClause += ' + $' + key + '.quantity' numLegsClause += ' + $' + key + '.quantity * $' + key + '.numLegs' whenClauses += ' )\n' } else { whenClauses += '\n quantity' + numAnimalsClause + ' == ' + totalAnimals + ',' whenClauses += '\n quantity * numLegs' + numLegsClause + ' == ' + totalLegs whenClauses += '\n )\n' } } …

…Tortoises & Cranes: DSL… … def drl = ''' dialect "mvel" rule "deduce animal counts" when ''' + whenClauses + ''' then ''' + thenClauses + '''end ''' def kbuilderConf = newKnowledgeBuilderConfiguration(null, loader) def kbuilder = newKnowledgeBuilder(kbuilderConf) kbuilder.add(newReaderResource(new StringReader(drl)), ResourceType.DRL) def kbaseConf = newKnowledgeBaseConfiguration(null, loader) def kbase = newKnowledgeBase(kbaseConf) kbase.addKnowledgePackages(kbuilder.knowledgePackages) def ksession = kbase.newStatefulKnowledgeSession() (totalAnimals + 1).times { n -> animals.each { key, val -> def capKey = key.capitalize() Class animal = loader.loadClass(capKey) if (totalLegs.intdiv(animal.numLegs) >= n) { ksession.insert(animal.newInstance(n)) } } } ksession.fireAllRules() ksession.dispose() } } …

…Tortoises & Cranes: DSL… … @Field animalProps = [:] def props = [:] def methodMissing(String name, _have) { new AnimalHolder(animals: animalProps, name: name) } def propertyMissing(String name) { name } class ThereHolder { def props def methodMissing(String name, args) { props['total' + args[0].capitalize()] = name.toInteger() } } class AnimalHolder { def animals, name def methodMissing(String number, args) { animals[name] = number.toInteger() } } def there = { _are -> new ThereHolder(props: props) }

…Tortoises & Cranes: DSL … cranes have 2 legs tortoises have 4 legs //millipedes have 1000 legs there are 7 animals //there are 8 animals there are 20 legs //there are 1020 legs new GroovyShell([animals: animalProps] as Binding).evaluate( animalProps.collect { key, val -> def capKey = key.capitalize() """ @groovy.transform.Immutable class $capKey { static int numLegs = $val int quantity } """ }.join('\n') + "Solver.main(animals, $props.totalAnimals, $props.totalLegs, getClass().classLoader)" )

Cranes 4

Tortoises 3

Cranes 4

Tortoises 3

Millipedes 1

Topics



• DSLs in Groovy

• Why Groovy?


Einstein’s Riddle


• More Info

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Einstein’s Riddle…

• Wikipedia: The zebra puzzle is a well-

known logic puzzle – It is often called Einstein's Puzzle or Einstein's Riddle

because it is said to have been invented by Albert

Einstein as a boy, with the claim that Einstein said

“… only 2 percent of the world's population can solve it.”

– The puzzle is also sometimes attributed to Lewis Carroll.

However, there is no known evidence for Einstein's or

Carroll's authorship; and the original puzzle cited

mentions brands of cigarette, such as Kools, that did not

exist during Carroll's lifetime or Einstein's boyhood

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…Einstein’s Riddle

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• Some premises: – The British person lives in the red house

– The Swede keeps dogs as pets

– The Dane drinks tea

– The green house is on the left of the white house

– The green homeowner drinks coffee

– The man who smokes Pall Mall keeps birds

– The owner of the yellow house smokes Dunhill

– The man living in the center house drinks milk

– The Norwegian lives in the first house

– The man who smokes Blend lives next to the one who keeps cats

– The man who keeps the horse lives next to the man who smokes Dunhill

– The man who smokes Bluemaster drinks beer

– The German smokes Prince

– The Norwegian lives next to the blue house

– The man who smokes Blend has a neighbor who drinks water

• And a question: – Who owns the fish?

Einstein’s Riddle : Prolog

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% from http://www.baptiste-wicht.com/2010/09/solve-einsteins-riddle-using-prolog % Preliminary definitions persons(0, []) :- !. persons(N, [(_Men,_Color,_Drink,_Smoke,_Animal)|T]) :- N1 is N-1, persons(N1,T). person(1, [H|_], H) :- !. person(N, [_|T], R) :- N1 is N-1, person(N1, T, R). % The Brit lives in a red house hint1([(brit,red,_, _, _)|_]). hint1([_|T]) :- hint1(T). % The Swede keeps dogs as pets hint2([(swede,_,_,_,dog)|_]). hint2([_|T]) :- hint2(T). % The Dane drinks tea hint3([(dane,_,tea,_,_)|_]). hint3([_|T]) :- hint3(T). % The Green house is on the left of the White house hint4([(_,green,_,_,_),(_,white,_,_,_)|_]). hint4([_|T]) :- hint4(T). % The owner of the Green house drinks coffee. hint5([(_,green,coffee,_,_)|_]). hint5([_|T]) :- hint5(T). ...

Einstein’s Riddle : Polyglot

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@GrabResolver('http://dev.inf.unideb.hu:8090/archiva/repository/internal') //@Grab('jlog:jlogic-debug:1.3.6') @Grab('org.prolog4j:prolog4j-api:0.2.0') // uncomment one of the next three lines //@Grab('org.prolog4j:prolog4j-jlog:0.2.0') @Grab('org.prolog4j:prolog4j-tuprolog:0.2.0') //@Grab('org.prolog4j:prolog4j-jtrolog:0.2.0') import org.prolog4j.* def p = ProverFactory.prover p.addTheory(new File('/GroovyExamples/tuProlog/src/einstein.pl').text) def sol = p.solve("solution(Persons).") //println sol.solution.get('Persons') // jlog to avoid converter println sol.get('Persons') // jtrolog/tuProlog

Einstein’s Riddle : Polyglot w/ DSL…

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// define some domain classes and objects enum Pet { dog, cat, bird, fish, horse } enum Color { green, white, red, blue, yellow } enum Smoke { dunhill, blends, pallmall, prince, bluemaster } enum Drink { water, tea, milk, coffee, beer } enum Nationality { Norwegian, Dane, Brit, German, Swede } dogs = dog; birds = bird; cats = cat; horses = horse a = owner = house = the = abode = person = man = is = to = side = next = who = different = 'ignored'

// some preliminary definitions p = ProverFactory.prover hintNum = 1 p.addTheory(''' persons(0, []) :- !. persons(N, [(_Men,_Color,_Drink,_Smoke,_Animal)|T]) :- N1 is N-1, persons(N1,T). person(1, [H|_], H) :- !. person(N, [_|T], R) :- N1 is N-1, person(N1, T, R). ''')

…Einstein’s Riddle : Polyglot w/ DSL…

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// define some helper methods (our interface to prolog) def addPairHint(Map m) { def from = m.from?.toString()?.toLowerCase() p.addTheory(""" hint$hintNum([(${from ?: '_'},${m.color ?: '_'},${m.drink ?: '_'},${m.smoke ?: '_'},${m.pet ?: '_'})|_]). hint$hintNum([_|T]) :- hint$hintNum(T). """) hintNum++ }

def addPositionHint(Map m, int pos) { def from = m.from?.toString()?.toLowerCase() p.addTheory(""" hint$hintNum(Persons) :- person($pos, Persons, (${from ?: '_'},${m.color ?: '_'},${m.drink ?: '_'},${m.smoke ?: '_'},${m.pet ?: '_'})). """) hintNum++ }

def addToLeftHint(Map left, Map right) { p.addTheory(""" hint$hintNum([(_,$left.color,_,_,_),(_,$right.color,_,_,_)|_]). hint$hintNum([_|T]) :- hint$hintNum(T). """) hintNum++ } ...


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// now implement DSL in terms of helper methods def the(Nationality n) { def ctx = [from:n] [ drinks: { d -> addPairHint(ctx + [drink:d]) }, smokes: { s -> addPairHint(ctx + [smoke:s]) }, keeps: { p -> addPairHint(ctx + [pet:p]) }, rears: { p -> addPairHint(ctx + [pet:p]) }, owns:{ _the -> [first:{ house -> addPositionHint(ctx, 1) }] }, has:{ _a -> [pet: { a -> addPairHint(ctx + [pet:a]) }] + Color.values().collectEntries{ c -> [c.toString(), { _dummy -> addPairHint(ctx + [color:c]) } ] } }, lives: { _next -> [to: { _the -> Color.values().collectEntries{ c -> [c.toString(), { _dummy -> addNeighbourHint(ctx, [color:c]) } ] } }]} ] } ...


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// now define the DSL the man from the centre house drinks milk the Norwegian owns the first house the Dane drinks tea the German smokes prince the Swede keeps dogs // alternate ending: has a pet dog the Brit has a red house // alternate ending: red abode the owner of the green house drinks coffee the owner of the yellow house smokes dunhill the person known to smoke pallmall rears birds // other ending: keeps birds the man known to smoke bluemaster drinks beer the green house is on the left side of the white house the man known to smoke blends lives next to the one who keeps cats the man known to keep horses lives next to the man who smokes dunhill the man known to smoke blends lives next to the one who drinks water the Norwegian lives next to the blue house


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// now implement DSL in terms of helper methods def the(Nationality n) { def ctx = [from:n] [ drinks: { d -> addPairHint(ctx + [drink:d]) }, smokes: { s -> addPairHint(ctx + [smoke:s]) }, keeps: { p -> addPairHint(ctx + [pet:p]) }, ... ] } ...

the German smokes prince

the(German).smokes(prince)

n = German ctx = [from: German] [drinks: …, smokes: { s -> addPairHint([from: German, smoke: s]) }, keeps: …, … ] addPairHint([from: German, smoke: prince])


• Some parts of our DSL are automatically

statically inferred, e.g. typing ‘bl’ and then

asking for completion yields:

• But other parts are not known, e.g. the

word ‘house’ in the fragment below:

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‘house’ is key for a Map and could be any value

…Einstein’s Riddle : Polyglot w/ DSL

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class HousePlaceHolder { def c1, script def house(_is) { [on: { _the -> [left: { _side -> [of: { __the -> Color.values().collectEntries { c2 -> [c2.toString(), { _dummy -> script.addToLeftHint( [color: c1], [color: c2] )}]} }]}]}] } } def the(Color c1) { new HousePlaceHolder(c1:c1, script:this) }

def the(Color c1) {[ house: { _is -> [on: { _the -> [left: { _side -> [of: { __the -> Color.values().collectEntries{ c2 -> [c2.toString(), { _dummy -> addToLeftHint([color:c1], [color:c2]) }]} }]}]}]} ]}

‘house’ is now understood

We can choose to introduce

additional static typing

information into our DSL

implementation or ‘teach’

our IDE about or DSL.

Einstein’s Riddle : Choco DSL…

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//@GrabResolver('http://www.emn.fr/z-info/choco-repo/mvn/repository') //@Grab('choco:choco-solver:2.1.5') import static choco.Choco.* import choco.kernel.model.variables.integer.* import groovy.transform.Field enum Pet { dog, cat, bird, fish, horse } enum Color { green, white, red, blue, yellow } enum Sport { baseball, volleyball, football, hockey, tennis } enum Drink { water, tea, milk, coffee, beer } enum Nationality { Norwegian, Dane, Briton, German, Swede } import static Pet.* import static Color.* import static Sport.* import static Drink.* import static Nationality.* // define logic solver data structures num = 5 center = 2 first = 0 println "Solving Einstein's Riddle:" …

…Einstein’s Riddle : Choco DSL…

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… @Field m = new choco.cp.model.CPModel() def s = new choco.cp.solver.CPSolver() choco.Choco.metaClass.static.eq = { c, v -> delegate.eq(c, v.ordinal()) } def makeEnumVar(st, arr) { choco.Choco.makeIntVar(st, 0, arr.size()-1, choco.Options.V_ENUM) } pets = new IntegerVariable[num] colors = new IntegerVariable[num] plays = new IntegerVariable[num] drinks = new IntegerVariable[num] nations = new IntegerVariable[num] (0..<num).each { i -> pets[i] = makeEnumVar("pet$i", pets) colors[i] = makeEnumVar("color$i", colors) plays[i] = makeEnumVar("plays$i", plays) drinks[i] = makeEnumVar("drink$i", drinks) nations[i] = makeEnumVar("nation$i", nations) } def pretty(s, c, arr, i) { c.values().find{ it.ordinal() == s.getVar(arr[i])?.value } } …


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… // define DSL (simplistic non-refactored version) def neighbours(var1, val1, var2, val2) { m.addConstraint and( ifOnlyIf(eq(var1[0], val1), eq(var2[1], val2)), implies(eq(var1[1], val1), or(eq(var2[0], val2), eq(var2[2], val2))), implies(eq(var1[2], val1), or(eq(var2[1], val2), eq(var2[3], val2))), implies(eq(var1[3], val1), or(eq(var2[2], val2), eq(var2[4], val2))), ifOnlyIf(eq(var1[4], val1), eq(var2[3], val2)) ) } iff = { e1, c1, e2, c2 -> m.addConstraint and(*(0..<num).collect{ ifOnlyIf(eq(e1[it], c1), eq(e2[it], c2)) }) } isEq = { a, b -> m.addConstraint eq(a, b) } dogs = dog; birds = bird; cats = cat; horses = horse a = owner = house = the = abode = person = man = to = is = side = next = who = different = 'ignored' …


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… // define the DSL in terms of DSL implementation def the(Nationality n) { def ctx = [nations, n] [ drinks:iff.curry(*ctx, drinks), plays:iff.curry(*ctx, plays), keeps:iff.curry(*ctx, pets), rears:iff.curry(*ctx, pets), owns:{ _the -> [first:{ house -> isEq(nations[first], n)}] }, has:{ _a -> [pet:iff.curry(*ctx, pets)] + Color.values().collectEntries{ c -> [c.toString(), { _dummy -> iff(*ctx, colors, c) } ] } }, lives: { _next -> [to: { _the -> Color.values().collectEntries{ c -> [c.toString(), { _dummy -> neighbours(*ctx, colors, c) } ] } }]} ] } …


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… def the(Color c1) {[ house: { _is -> [on: { _the -> [left: { _side -> [of: { __the -> Color.values().collectEntries{ c2 -> [c2.toString(), { _dummy -> m.addConstraint and(*(1..<num).collect{ ifOnlyIf(eq(colors[it-1], c1), eq(colors[it], c2)) }) }]} }]}]}]} ]} def the(String _dummy) {[ of:{ _the -> Color.values().collectEntries{ c -> [c.toString(), { _house -> [ drinks:iff.curry(colors, c, drinks), plays:iff.curry(colors, c, plays) ] } ] } }, known: { _to -> [ play: { sport -> def ctx = [plays, sport] [ rears: iff.curry(*ctx, pets), keeps: iff.curry(*ctx, pets), drinks: iff.curry(*ctx, drinks), lives: { _next -> [to: { _the -> [one: { _who -> [ keeps: { pet -> neighbours(pets, pet, *ctx) }, drinks: { beverage -> neighbours(drinks, beverage, *ctx) } ]}]}]} ] }, …


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… keep : { pet -> [ lives: { _next -> [to: { _the -> [man: { _who -> [ plays: { sport -> neighbours(pets, pet, plays, sport) } ]}]}]} ]} ]}, from: { _the -> [center: { house -> [drinks: { d -> isEq(drinks[center], d)}] }]} ]} def all(IntegerVariable[] var) { [are: { _different -> m.addConstraint allDifferent(var) } ] } …

…Einstein’s Riddle : Choco DSL

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… // define rules all pets are different all colors are different all plays are different all drinks are different all nations are different the man from the center house drinks milk the Norwegian owns the first house the Dane drinks tea the German plays hockey the Swede keeps dogs // alternate ending: has a pet dog the Briton has a red house // alternate ending: red abode the owner of the green house drinks coffee the owner of the yellow house plays baseball the person known to play football rears birds // alternate ending: keeps birds the man known to play tennis drinks beer the green house is on the left side of the white house the man known to play volleyball lives next to the one who keeps cats the man known to keep horses lives next to the man who plays baseball the man known to play volleyball lives next to the one who drinks water the Norwegian lives next to the blue house …

…Einstein’s Riddle : Choco…

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… // invoke logic solver s.read(m) def more = s.solve() while (more) { for (i in 0..<num) { print 'The ' + pretty(s, Nationality, nations, i) print ' has a pet ' + pretty(s, Pet, pets, i) print ' plays ' + pretty(s, Sport, plays, i) print ' drinks ' + pretty(s, Drink, drinks, i) println ' and lives in a ' + pretty(s, Color, colors, i) + ' house' } more = s.nextSolution() }

Einstein’s Riddle : Output

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Solving Einstein's Riddle: The Norwegian has a pet cat plays baseball drinks water and lives in a yellow house The Dane has a pet horse plays volleyball drinks tea and lives in a blue house The Briton has a pet bird plays football drinks milk and lives in a red house The German has a pet fish plays hockey drinks coffee and lives in a green house The Swede has a pet dog plays tennis drinks beer and lives in a white house

Discussion points

• Choosing granularity

• Choosing the level of dynamic/static typing

• Multi-paradigm solutions

• Capturing Rule Design Patterns using AST

transforms

Granularity

Solve manners2009

Neighbours must share a hobby Neighbours are of a different gender There should be 2 doctors at each table Each doctor at a table should be a different kind ...

The Guest at position 2 on table 1 should have a different gender to the Guest at position 1 The Guest at position 2 on table 1 should have a different gender to the Guest at position 3 ...

Typing…

• Dynamic

• Traditional Static Typing

• Stronger levels of Static Typing

…Typing…

import groovy.transform.TypeChecked import experimental.SprintfTypeCheckingVisitor @TypeChecked(visitor=SprintfTypeCheckingVisitor) void main() { sprintf('%s will turn %d on %tF', 'John', new Date(), 21) }

[Static type checking] - Parameter types didn't match types expected from the format String: For placeholder 2 [%d] expected 'int' but was 'java.util.Date' For placeholder 3 [%tF] expected 'java.util.Date' but was 'int'

sprintf has an Object varargs

parameter, hence not normally

amenable to further static checking

but for constant Strings we can do

better using a custom type checking

plugin.

…Typing…

import groovy.transform.TypeChecked import tictactoe.* Import static tictactoe.Position.* @TypeChecked(visitor=TicTacToeTypeVisitor) void main() { Board.empty().move(NW).move(C).move(W).move(SW).move(SE) }

package tictactoe enum Position { NW, N, NE, W, C, E, SW, S, SE } class Board { static Board empty() { new Board() } Board move(Position p) { this } }

…Typing

import groovy.transform.TypeChecked import tictactoe.* Import static tictactoe.Position.* @TypeChecked(visitor=TicTacToeTypeVisitor) void main() { Board.empty().move(NW).move(C).move(W).move(SW).move(SE) }

package tictactoe enum Position { NW, N, NE, W, C, E, SW, S, SE }

[Static type checking] - Attempt to call suboptimal move SE not allowed [HINT: try NE]

Custom type checker which fails

compilation if programmer attempts

to code a suboptimal solution. Where

suboptimal means doesn’t agree with

what is returned by a minimax,

alpha-beta pruning, iterative

deepening solving engine.

Multi-paradigm solutions

• Imperative

• Functional – Leveraging immutable data structures

– Persistent data structures

– Higher-order functions

• Rules-based

• Concurrency, e.g. Gpars – Data Parallelism: Map, Reduce

– DataFlow

– Others: Fork Join, Actors

Using compile-time Metaprogramming

• Powerful mechanism – As illustrated by GOF examples

– @Immutable, @Delegate and others

• Rich area for further research – Explore whether rules design patterns can be readily

embodied within AST transforms

More Information: URLs

• Groovy – http://groovy.codehaus.org/

• Groovy DSL talk in general – http://www.slideshare.net/glaforge/groovy-domain-specific-

languages-springone2gx-2013

• Groovy & Other Paradigms – http://www.slideshare.net/paulk_asert/concurrency-with-gpars

– http://www.slideshare.net/paulk_asert/functional-groovy

• Drools Expert & Planner – http://www.jboss.org/drools/

• Choco – http://www.emn.fr/z-info/choco-solver/

More Information: Groovy in Action 2ed

Contains a

chapter on

DSLs!

groovy rules

Technology