groovy DSLs from beginner to expert

Chicago, October 19 - 22, 2010
Paul King
@paulk_asert
Groovy Committer
ASERT, Australia
Groovy.DSLs(from: beginner,
to: expert)
Guillaume Laforge
@glaforge
Groovy Project Manager
SpringSource / VMWare

Topics
Introduction
• Groovy DSL Features
• A Week In The Life Of DSL INC
• Summary
• More Info
DSLs 2010 - 2
©ASERT2006-2010

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
– In contrast, general-purpose languages are created to solve
problems in many domains
– Somewhere between declarative data and a full blown 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
©ASERT2006-2010

Technical Examples
Source: Applying minilanguages: http://www.faqs.org/docs/artu/ch08s02.html
<?xml version="1.0"?>
<xsl:stylesheetversion="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml"/>
<xsl:template match="*">
<xsl:element name="{name()}">
<xsl:for-each select="@*">
<xsl:element name="{name()}">
<xsl:value-of select="."/>
</xsl:element>
</xsl:for-each>
<xsl:apply-templates select="*|text()"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
cat thesis.ms | chem | tbl | refer | grap | pic | eqn | groff -Tps > thesis.ps
<?xml version="1.0"?>
<GTK-Interface>
<widget>
<class>GtkWindow</class>
<name>HelloWindow</name>
<border_width>5</border_width>
<Signal>
<name>destroy</name>
<handler>gtk_main_quit</handler>
</Signal>
<title>Hello</title>
<type>GTK_WINDOW_TOPLEVEL</type>
<position>GTK_WIN_POS_NONE</position>
<allow_shrink>True</allow_shrink>
<allow_grow>True</allow_grow>
<auto_shrink>False</auto_shrink>
<widget>
<class>GtkButton</class>
<name>Hello World</name>
<can_focus>True</can_focus>
<label>Hello World</label>
</widget>
</widget>
</GTK-Interface>
# Poll this site first each cycle.
poll pop.provider.net proto pop3
user "jsmith" with pass "secret1" is "smith" here
user jones with pass "secret2" is "jjones" here with options keep
# Poll this site second, unless Lord Voldemort zaps us first.
poll billywig.hogwarts.com with proto imap:
user harry_potter with pass "floo" is harry_potter here
# Poll this site third in the cycle.
# Password will be fetched from ~/.netrc
poll mailhost.net with proto imap:
user esr is esr here
Glade
Troff
XSLT
fetchmail
Regex
"x.z?z{1,3}y"
SQL
SELECT * FROM TABLE
WHERE NAME LIKE '%SMI'
ORDER BY NAME
DSLs 2010 - 7

Origins
• It has always been a
holy grail of computer
users to be able to
speak directly to our
computers
• Different languages have pushed the
boundaries further than others
– APT for numerically controlled machine tools (1957)
– BNF (1959), COBOL, 4GLs
– LISP & Smalltalk
– Unix "little languages"
DSLs 2010 - 8
©ASERT2006-2010

Origins
• It has always been a
holy grail of computer
users to be able to
speak directly to our
computers
DSLs 2010 - 9
http://dsal.uchicago.edu/reference/gazetteer/pager.html?objectid=DS405.1.I34_V02_298.gif
©ASERT2006-2010

Origins: LISP & Smalltalk
“In Lisp, you don’t just write your
program down toward the language,
you also build the language up
toward your program”
- Paul Graham
“When [Smalltalk] is used to
describe an application system, the
developer extends Smalltalk,
creating a domain-specific language
by adding a new vocabulary of
language elements ...”
- Adele Goldberg
DSLs 2010 - 10
©ASERT2006-2010

Origins: Minilanguages...
Source: The Art of Unix Programming:Taxonomy of languages: http://www.faqs.org/docs/artu/ch08s01.html
%!PS-Adobe-3.0
%%Creator: groff version 1.20.1
...
597.6 12 72 12 DL(increasing loopiness)297.71 8.2 Q(/etc/passwd)102.67
94.6 Q(.ne)110.715 106.6 Q(wsrc)-.25 E(SNG)195.2 100.6 Q(re)243.8 94.6 Q
(ge)-.15 E(xps)-.15 E(Glade)247.26 106.6 Q(m4)306.81 58.6 Q -1(Ya)303.43
70.6 S(cc)1 E(Le)305.5 82.6 Q(x)-.15 E(mak)302.42 94.6 Q(e)-.1 E(XSL)
301.16 106.6 Q(T)-.92 E(pic)307.09 118.6 Q(tbl)307.92 130.6 Q(eqn)305.98
142.6 Q(fetchmail)344.715 82.6 Q -.15(aw)355.345 94.6 S(k).15 E(trof)
354.84 106.6 Q(f)-.25 E(Postscript)343.875 118.6 Q(dc)412.88 94.6 Q(bc)
412.88 106.6 Q(Emacs Lisp)462.53 94.6 Q(Ja)465.395 106.6 Q -.25(va)-.2 G
(Script).25 E(sh)529.075 94.6 Q(tcl)528.52 106.6 Q(Perl)565.065 88.6 Q
(Python)558.95 100.6 Q(Ja)564.46 112.6 Q -.25(va)-.2 G 0 Cg EP
%%Trailer
end
%%EOF
Input DSL: pic for above picture Output "DSL": Postscript for above picture
# Minilanguage taxonomy
# Base ellipses
define smallellipse {ellipse width 3.0 height 1.5}
M: ellipse width 3.0 height 1.8 fill 0.2
line from M.n to M.s dashed
D: smallellipse() with .e at M.w + (0.8, 0)
line from D.n to D.s dashed
I: smallellipse() with .w at M.e - (0.8, 0)
# Arrow headings
arrow from D.w + (0.4, 0.8) to D.e + (-0.4, 0.8)
"flat to structured" "" at last arrow.c
...
# Interpreters
"Emacs Lisp" "JavaScript" at 0.25 between M.e and I.e
"sh" "tcl" at 0.55 between M.e and I.e
"Perl" "Python" "Java" at 0.8 between M.e and I.e
DSLs 2010 - 11

...Origins: Minilanguages
PowerPoint DSL for previous slide
import builder.PowerPointBuilder
def name = 'minilanguages'
assert new File("${name}.pic').exists()
"groff -e -p ${name}.pic > ${name}.ps".execute()
"gs -q -sDEVICE='ppmraw' -g2600x3500 -r300x300 -sOutputFile='-' -dBATCH ↵
–dNOPAUSE ${name}.ps | pnmcrop | ppmtogif > ${name}.gif".execute()
def builder = new PowerPointBuilder() // Adapted from Erik Pragt
builder.slideshow(filename: 'DSLsInGroovy_MiniLanguages.ppt') {
slide(title: 'Origins: Minilanguages...') {
image(
origin: [0, 15],
src: "${name}.gif",
caption: 'Source: The Art of Unix Programming:Taxonomy...' )
textbox(
origin: [5, 100],
text: new File("${name}.pic").text,
caption: 'Input DSL: pic for above picture' )
textbox(
origin: [115, 100],
text: new File("${name}.ps").text,
caption: 'Output "DSL": Postscript for above picture' )
}
}
DSLs 2010 - 12

Subject Matter Experts,
Business Analysts...

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
Developer producing LOLCODE

And in the end...
nobody understands
each other

DSL: a potential solution?
1616
• Use a more expressive language than a
general purpose one
• Share a common metaphor of
understanding between developers and
subject matter experts
• Have domain experts help with the design
of the business logic of an application
• Avoid cluttering business code with
too much boilerplate technical code
• Cleanly separate business logic from
application code
• Let business rules have their own lifecycle

17
Copyright 2010 SpringSource. Copying, publishing or distributing without express written permission is prohibited.
Towards more readibility (1)
20%
17

18
Towards more readibility (2)
80%

Why a DSL?
• Advantages:
– Domain experts can
understand, validate, modify,
and often even develop DSL
programs
– Somewhat self-documenting
– Enhance quality,
productivity, reliability,
maintainability, portability
and reusability
– Safety; as long as the
language constructs are safe
any sentence written with
them can be considered safe
• Disadvantages:
– Learning cost vs. limited
applicability
– Cost of designing,
implementing & maintaining
DSL as well as the tools/IDEs
– Attaining proper scope
– Trade-offs between domain-
specificity and general-
purpose programming
language constructs
– Efficiency costs
– Proliferation of similar non-
standard DSLs, i.e. different
but similar DSLs used within
two insurance companies
Source: http://en.wikipedia.org/wiki/Domain-specific_language DSLs 2010 - 19
©ASERT2006-2010

DSL usage patterns...
• Internal (uses a general purpose language)
– AKA embedded
– Can be a subset or superset
– Can be generated/converted from other "language"
– Numerous mechanisms to make as close to the
domain as possible
• External (custom language)
– May involve writing your own traditional parser
– Using parser combinators
– Interpreting
– String grepping
• Other characteristics
– Functional vs OO
DSLs 2010 - 20
©ASERT2006-2010

...DSL usage patterns...
Source: DSLs in Action, Debasish Ghosh, Manning now in MEAP DSLs 2010 - 21
©ASERT2006-2010

...DSL usage patterns
Source: DSLs in Action, Debasish Ghosh, Manning now in MEAP DSLs 2010 - 22
©ASERT2006-2010

DSL usage patterns (Advanced)
Source: http://www.spinellis.gr/pubs/jrnl/2000-JSS-DSLPatterns/html/dslpat.html
See: Diomidis Spinellis. Notable design patterns for domain specific languages. Journal of Systems and Software, 56(1):91–99, February 2001.
©ASERT2006-2010

DSLs 2010 - 24
©ASERT2006-2010
What is Groovy?
• “Groovy is like a super version
of Java. It can leverage Java's
enterprise capabilities but also
has cool productivity features like closures,
DSL support, builders and dynamic typing.”
Groovy = Java – boiler plate code
+ optional dynamic typing
+ closures
+ domain specific languages
+ builders
+ metaprogramming

DSLs 2010 - 25
©ASERT2006-2010
Groovy Goodies Overview
• Fully object oriented
• Closures: reusable
and assignable
pieces of code
• Operators can be
overloaded
• Multimethods
• Literal declaration for
lists (arrays), maps,
ranges and regular
expressions
• GPath: efficient
object navigation
• GroovyBeans
• grep and switch
• Templates, builder,
swing, Ant, markup,
XML, SQL, XML-RPC,
Scriptom, Grails,
tests, Mocks

Growing Acceptance …
A slow and steady start but now gaining in
momentum, maturity and mindshare
Now free

DSLs 2010 - 27
©ASERT2006-2010
The Landscape of JVM Languages
Java bytecode calls
for static types
Dynamic features call
for dynamic types
optional
static
types
The terms “Java Virtual Machine” and “JVM” mean a Virtual Machine for the Java™ platform.

DSLs 2010 - 28
©ASERT2006-2010
Groovy Starter
System.out.println("Hello, World!"); // supports Java syntax
println 'Hello, World!' // but can remove some syntax
String name = 'Guillaume' // Explicit typing/awareness
println "$name, I'll get the car." // Gstring (interpolation)
def longer = """${name}, the car
is in the next row.""" // multi-line, implicit type
assert 0.5 == 1/2 // BigDecimal equals()
assert 0.1 + 0.2 == 0.3 // and arithmetic
def printSize(obj) { // implicit/duck typing
print obj?.size() // safe dereferencing
}
def pets = ['ant', 'bee', 'cat'] // native list syntax
pets.each { pet -> // closure support
assert pet < 'dog' // overloading '<' on String
} // or: for (pet in pets)...

A Better Java...
DSLs 2010 - 29
©ASERT2006-2010
import java.util.List;
import java.util.ArrayList;
class Erase {
private List removeLongerThan(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);
Erase e = new Erase();
List shortNames = e.removeLongerThan(names, 3);
System.out.println(shortNames.size());
for (int i = 0; i < shortNames.size(); i++) {
String s = (String) shortNames.get(i);
System.out.println(s);
}
}
}
This code
is valid
Java and
valid Groovy
Based on an
example by
Jim Weirich
& Ted Leung

...A Better Java...
DSLs 2010 - 30
©ASERT2006-2010
import java.util.List;
import java.util.ArrayList;
class Erase {
List result = new ArrayList();
for (int i = 0; i < strings.size(); i++) {
String s = (String) strings.get(i);
result.add(s);
}
}
return result;
}
List names = new ArrayList();
names.add("Ted"); names.add("Fred");
names.add("Jed"); names.add("Ned");
System.out.println(names);
Erase e = new Erase();
List shortNames = e.removeLongerThan(names, 3);
System.out.println(shortNames.size());
for (int i = 0; i < shortNames.size(); i++) {
String s = (String) shortNames.get(i);
System.out.println(s);
}
}
}
Do the
semicolons
add anything?
And shouldn‟t
we us more
modern list
notation?
Why not
import common
libraries?

...A Better Java...
DSLs 2010 - 31
©ASERT2006-2010
class Erase {
List result = new ArrayList()
for (String s in strings) {
result.add(s)
}
}
return result
}
List names = new ArrayList()
names.add("Ted"); names.add("Fred")
names.add("Jed"); names.add("Ned")
System.out.println(names)
Erase e = new Erase()
List shortNames = e.removeLongerThan(names, 3)
System.out.println(shortNames.size())
for (String s in shortNames) {
System.out.println(s)
}
}
}

...A Better Java...
DSLs 2010 - 32
©ASERT2006-2010
class Erase {
List result = new ArrayList()
for (String s in strings) {
result.add(s)
}
}
return result
}
List names = new ArrayList()
names.add("Ted"); names.add("Fred")
names.add("Jed"); names.add("Ned")
Erase e = new Erase()
List shortNames = e.removeLongerThan(names, 3)
for (String s in shortNames) {
}
}
}
Do we need
the static types?
Must we always
have a main
method and
class definition?
How about
improved
consistency?

...A Better Java...
DSLs 2010 - 33
©ASERT2006-2010
def removeLongerThan(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")
shortNames = removeLongerThan(names, 3)
for (s in shortNames) {
}

...A Better Java...
DSLs 2010 - 34
©ASERT2006-2010
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")
for (s in shortNames) {
}
Shouldn‟t we
have special
notation for lists?
And special
facilities for
list processing?
Is „return‟
needed at end?

...A Better Java...
DSLs 2010 - 35
©ASERT2006-2010
strings.findAll{ it.size() <= length }
}
names = ["Ted", "Fred", "Jed", "Ned"]
shortNames.each{ System.out.println(s) }

...A Better Java...
DSLs 2010 - 36
©ASERT2006-2010
strings.findAll{ it.size() <= length }
}
shortNames.each{ System.out.println(s) }
Is the method
now needed?
Easier ways to
use common
methods?
Are brackets
required here?

...A Better Java...
DSLs 2010 - 37
©ASERT2006-2010
println names
shortNames = names.findAll{ it.size() <= 3 }
println shortNames.size()
shortNames.each{ println it }

...A Better Java
DSLs 2010 - 38
©ASERT2006-2010
println names
shortNames = names.findAll{ it.size() <= 3 }
println shortNames.size()
shortNames.each{ println it }
["Ted", "Fred", "Jed", "Ned"]
3
Ted
Jed
Ned

Grapes / Grab
DSLs 2010 - 39
©ASERT2006-2010
// Google Collections example
@Grab('com.google.collections:google-collections:1.0')
import com.google.common.collect.HashBiMap
HashBiMap fruit =
[grape:'purple', lemon:'yellow', lime:'green']
assert fruit.lemon == 'yellow'
assert fruit.inverse().yellow == 'lemon'

Malleable Syntax
DSLs 2010 - 40
©ASERT2006-2010
order to buy 200.shares of GOOG {
limitPrice 500
allOrNone false
at the value of { qty * unitPrice - 100 }
}
take 2.pills of chloroquinine after 6.hours
Groovy 1.8+
def "length of Spock's & his friends' names"() {
expect:
name.size() == length
where:
name | length
"Spock" | 5
"Kirk" | 4
"Scotty" | 6
}

41
Real-life Groovy DSL 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...

42
DSLs within the Groovy Ecosystem
• Testing DSLs
– EasyB, Spock, JBehave, …
• Builders
– MarkupBuilder, SwingBuilder
• Build Tool DSLs
– AntBuilder, Gant, Gradle
• Grails
– BeanBuilder, Criteria, ConfigSlurper
• GPars
– DSL for concurrent activities
• and more...

Testing DSLs: Spock...
©ASERT2006-2010
DSLs 2010 - 43

...Testing DSLs: Spock...
©ASERT2006-2010
• Testing framework for Java and Groovy
• Highly expressive specification language
– No assertion API
– No record &
replay
mocking API
– No
superfluous
annotations
– Meaningful
assert error
messages
– Extensible
– Compatible
with JUnit
reportingwise
@Speck
@RunWith(Sputnik)
class PublisherSubscriberSpeck {
def "events are received by all subscribers"() {
def pub = new Publisher()
def sub1 = Mock(Subscriber)
def sub2 = Mock(Subscriber)
pub.subscribers << sub1 << sub2
when:
pub.send("event")
then:
1 * sub1.receive("event")
1 * sub2.receive("event")
}
}
DSLs 2010 - 44

...Testing DSLs: Spock...
©ASERT2006-2010
import com.gargoylesoftware.htmlunit.WebClient
import spock.lang.*
import org.junit.runner.RunWith
@Speck ()
@RunWith (Sputnik)
class TestSimpBlogSpock {
def page, subheadings, para, form, result
@Unroll("When #author posts a #category blog with content '#content' it sho
def "when creating a new blog entry"() {
given:
page = new WebClient().getPage('http://localhost:8080/postForm')
form = page.getFormByName('post')
when:
form.getInputByName('title').setValueAttribute("$author was here (and s
form.getSelectByName('category').getOptions().find { it.text == categor
form.getSelectByName('author').getOptions().find { it.text == author }.
form.getTextAreaByName('content').setText(content)
result = form.getInputByName('btnPost').click()
subheadings = result.getElementsByTagName('h3')
para = result.getByXPath('//TABLE//TR/TD/P')[0]
...
DSLs 2010 - 45

... Testing DSLs: Spock
©ASERT2006-2010
...
then:
page.titleText == 'Welcome to SimpBlog'
result.getElementsByTagName('h1').item(0).textContent.matches("Post.*: $au
subheadings.item(1).textContent == "Category: $category"
subheadings.item(2).textContent == "Author: $author"
and:
para.textContent == content
where:
author << ['Bart', 'Homer', 'Lisa']
category << ['Home', 'Work', 'Food']
content << ['foo', 'bar', 'baz']
}
}
// Optional use of 'and:'
DSLs 2010 - 46

©ASERT2006-2010
Testing DSLs: EasyB…
• Description: BDD, Rspec-like testing library
narrative 'segment flown', {
as_a 'frequent flyer'
i_want 'to accrue rewards points for every segment I fly'
so_that 'I can receive free flights for my dedication to the airline'
}
scenario 'segment flown', {
given 'a frequent flyer with a rewards balance of 1500 points'
when 'that flyer completes a segment worth 500 points'
then 'that flyer has a new rewards balance of 2000 points'
}
given 'a frequent flyer with a rewards balance of 1500 points', {
flyer = new FrequentFlyer(1500)
}
when 'that flyer completes a segment worth 500 points', {
flyer.fly(new Segment(500))
}
then 'that flyer has a new rewards balance of 2000 points', {
flyer.pointsBalance.shouldBe 2000
}
}
DSLs 2010 - 47

…Testing DSLs: EasyB
• When run will be marked as pending
– perfect for ATDD
©ASERT2006-2010
scenario "Bart posts a new blog entry", {
given "we are on the create blog entry page"
when "I have entered 'Bart was here' as the title"
and "I have entered 'Cowabunga Dude!' into the content"
and "I have selected 'Home' as the category"
and "I have selected 'Bart' as the author"
and "I click the 'Create Post' button"
then "I expect the entry to be posted"
}
DSLs 2010 - 48

Testing DSLS: Cucumber...
©ASERT2006-2010
# language: en
@newpost
Feature: New Blog Post
In order to create a new blog entry
Bloggers should be able to select their name and category and enter text
Scenario: New Posting
Given we are on the create blog entry page
When I have entered "Bart was here" as the title
And I have entered "Cowabunga Dude!" as the content
And I have selected "Home" from the "category" dropdown
And I have selected "Bart" from the "author" dropdown
And I click the 'Create Post' button
Then I should see a heading message matching "Post.*: Bart was here.*"
DSLs 2010 - 49

... Testing DSLS: Cucumber...
©ASERT2006-2010
DSLs 2010 - 50

...Testing DSLS: Cucumber
©ASERT2006-2010
import com.gargoylesoftware.htmlunit.WebClient
this.metaClass.mixin(cuke4duke.GroovyDsl)
Given ~/we are on the create blog entry page/, { ->
page = new WebClient().getPage('http://localhost:8080/postForm')
}
When(~/I have entered "(.*)" as the title/) {String title ->
form = page.getFormByName('post')
form.getInputByName('title').setValueAttribute(title + ' (and so was Cucumber)')
}
When(~'I have entered "(.*)" as the content') {String content ->
form.getTextAreaByName('content').setText(content)
}
When(~'I have selected "(.*)" from the "(.*)" dropdown') {String option, String name ->
form.getSelectByName(name).getOptions().find {
it.text == option }.setSelected(true)
}
When(~"I click the 'Create Post' button") { ->
result = form.getInputByName('btnPost').click()
}
Then(~'I should see a heading message matching "(.*)"') {String pattern ->
// ensureThat result.getElementsByTagName('h1').item(0).textContent.matches(pattern)
assert result.getElementsByTagName('h1').item(0).textContent.matches(pattern)
}
DSLs 2010 - 51

Grails Criteria
DSLs 2010 - 52
©ASERT2006-2010
// Account is a POJO in our domain/model
def c = Account.createCriteria()
def results = c {
like("holderFirstName", "Fred%")
and {
between("balance", 500, 1000)
eq("branch", "London")
}
maxResults(10)
order("holderLastName", "desc")
}
// source: Grails doco: 5. Object Relational Mapping (GORM): 5.4.2 Criteria

Grails Criteria Example
DSLs 2010 - 53
©ASERT2006-2010
// Book is a POJO in our domain/model
def book = Book.findByTitle("The Stand")
book = Book.findByTitleLike("Harry Pot%")
book = Book.findByReleaseDateBetween( firstDate, secondDate )
book = Book.findByReleaseDateGreaterThan( someDate )
book = Book.findByTitleLikeOrReleaseDateLessThan(
"%Something%", someDate )
books = Book.findAllByTitleLikeAndReleaseDateGreaterThan(
"%Java%", new Date()-30)
// source: Grails doco: 5. Object Relational Mapping (GORM): 5.4.1 Dynamic Finders

Grails Bean Builder Example
DSLs 2010 - 54
©ASERT2006-2010
bb.beans {
marge(Person) {
name = "marge"
husband = { Person p ->
name = "homer"
age = 45
props = [overweight:true, height:"1.8m"]
}
children = [bart, lisa]
}
bart(Person) {
name = "Bart"
age = 11
}
lisa(Person) {
name = "Lisa"
age = 9
}
}
// source: 14. Grails and Spring: 14.3 Runtime Spring with the Beans DSL

GPars...
import static org.gparallelizer.actors.pooledActors.PooledActors.*
// create a new actor that prints out received messages
def console = actor {
loop {
react {message ->
println message
}
}
}
// start the actor and send it a message
console.start()
console.send('Message')
DSLs 2010 - 55

...GPars
import static org.gparallelizer.dataflow.DataFlow.thread
final def x = new DataFlowVariable()
final def y = new DataFlowVariable()
final def z = new DataFlowVariable()
thread {
z << ~x + ~y
println "Result: ${~z}"
}
thread {
x << 10
}
thread {
y << 5
}
No race-conditions
No deadlocks
No live-locks
Completely deterministic programs
BEAUTIFUL code
DSLs 2010 - 56

Topics
• Introduction
Groovy DSL Features
• Summary
• More Info
DSLs 2010 - 57
©ASERT2006-2010

Groovy DSL Features
DSLs 2010 - 58
©ASERT2006-2010

Import / Import Static
• Imports
• Static Imports
DSLs 2010 - 59
©ASERT2006-2010
@Grab('com.google.collections:google-collections:1.0')
import com.google.common.collect.HashBiMap as HashMap
def m = new HashMap()
m.key = 'value'
assert m.inverse().value == 'key'
import static java.util.Calendar.getInstance as now
println now().format('yyyy/MMM/dd')
What Java gives us plus aliases

Static Imports...
DSLs 2010 - 60
©ASERT2006-2010
import groovy.swing.SwingXBuilder
import static java.awt.Color.*
import static java.lang.Math.*
def swing = new SwingXBuilder()
def frame = swing.frame(size: [300, 300]) {
graph(plots: [
[GREEN, {value -> sin(value)}],
[BLUE, {value -> cos(value)}],
[RED, {value -> tan(value)}]
])
}.show()
 Java Static Imports
Discussed later:
 Builders
 Closures

...Static Imports...
DSLs 2010 - 61
©ASERT2006-2010
graph(plots: [
])
}.show()
Java gives us this

DSLs 2010 - 62
©ASERT2006-2010
graph(plots: [
])
}.show()
Java gives us this

DSLs 2010 - 63
©ASERT2006-2010
Source: http://www.thedoghousediaries.com/?p=1406

...Static Imports
DSLs 2010 - 64
©ASERT2006-2010
import static java.awt.Color.GREEN as Lime
import static java.awt.Color.BLUE as Sky
import static java.awt.Color.RED as Maraschino
graph(plots: [
[Lime, {value -> sin(value)}],
[Sky, {value -> cos(value)}],
[Maraschino, {value -> tan(value)}]
])
}.show()
Java doesn‟t give us this!

Literal Syntax Conventions
• Lists
– Special syntax for list literals
– Additional common methods (operator overloading)
• Maps
– Special syntax for map literals
– Additional common methods
• Ranges
– Special syntax for various kinds of ranges
DSLs 2010 - 65
©ASERT2006-2010
def list = [3, new Date(), 'Jan']
assert list + list == list * 2
def map = [a: 1, b: 2]
assert map['a'] == 1 && map.b == 2
def letters = 'a'..'z'
def numbers = 0..<10

Literal Syntax Conventions in DSLs
DSLs 2010 - 66
©ASERT2006-2010
import static java.util.Calendar.getInstance as getNow
import static java.util.Calendar.*
def discount = [normal:0, silver:5, gold:10]
def roomrate = [weekday:150, weekend:95]
for (level in ['normal', 'silver', 'gold']) {
def multiplier = 1 - discount[level] / 100
print 'Your room rate is: '
if (now[DAY_OF_WEEK] in MONDAY..FRIDAY)
println roomrate.weekday * multiplier
else
println roomrate.weekend * multiplier
}
Your room rate is: 150
Your room rate is: 142.50
Your room rate is: 135.0
 Literal list & map syntax
 Ranges
Also
 Static import aliases
 BigDecimal arithmetic

Compact Syntax...
• Java
• Groovy
DSLs 2010 - 67
©ASERT2006-2010
public class BuySharesJava {
public static void buyShares(int qty, String name) {
// business logic here ...
System.out.println("buying " + qty
+ " shares of " + name);
}
buyShares(3, "BHP");
}
}
def buyShares(qty, name) {
// business logic here ...
println "buying $qty shares of $name"
}
buyShares 3, 'BHP'
 Script syntax
 Conventions for visibility
 GDK methods: println
 Implicit typing
 GString interpolation
 Optional brackets & „;‟

...Compact Syntax...
• Java
• Groovy
DSLs 2010 - 68
©ASERT2006-2010
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
public class ProcessCustomerJava {
public static void printDetails(Map<String, String> cust) {
System.out.println("Details as at: " + new Date());
String first = cust.get("first");
System.out.println("First name: " + first);
String last = cust.get("last");
System.out.println("Last name: " + (last != null ? last : "unknown"));
}
Map<String, String> details = new HashMap<String, String>();
details.put("first", "John");
details.put("last", "Smith");
printDetails(details);
}
} def printDetails(cust) {
println """Details as at: ${new Date()}
First name: $cust.first
Last name: ${cust.last ?: 'unknown'}"""
}
printDetails first: 'John', last: 'Smith'
 Script syntax, Named params, Extra imports
 Conventions for visibility, GDK methods
 Implicit typing, Multi-line GString
 Elvis operator, Optional brackets & „;‟

...Compact Syntax
• Java
• Groovy
DSLs 2010 - 69
©ASERT2006-2010
import java.util.Date;
public class ProcessStrongCustomerJava {
public static void printDetails(CustomerJ cust) {
System.out.println("Details as at: " + new Date());
String first = cust.getFirst();
System.out.println("First name: " + first);
String last = cust.getLast();
System.out.println("Last name: " + (last != null ? last : "unknown"));
}
CustomerJ c = new CustomerJ();
c.setFirst("John");
c.setLast("Smith");
printDetails(c);
}
}
class CustomerJ {
private String first;
private String last;
public String getFirst() {
return first;
}
public void setFirst(String first) {
this.first = first;
}
public String getLast() {
return last;
}
public void setLast(String last) {
this.last = last;
}
}
class CustomerG { String first, last }
def printDetails(cust) {
println """Details as at: ${new Date()}
First name: $cust.first
Last name: ${cust.last ?: 'unknown'}"""
}
printDetails new CustomerG(first: 'John',
last: 'Smith')
Plus:
 Named params for constructors
 JavaBean conventions
 Leverage Duck Typing

Using With Example
DSLs 2010 - 70
©ASERT2006-2010
letters = ['a', 'b', 'c']
range = 'b'..'d'
letters.with {
add 'd'
remove 'a'
}
assert letters == range
map = [a:10, b:4, c:7]
map.with {
assert (a + b) / c == 2
}
Just normal methods
for ArrayList here

Closures...
• Traditional mainstream languages
– Data can be stored in variables, passed around,
combined in structured ways to form more complex
data; code stays put where it is defined
• Languages supporting closures
– Data and code can be stored in variables, passed
around, combined in structured ways to form more
complex algorithms and data; functional coding style
DSLs 2010 - 71
©ASERT2006-2010
doubleNum = { num -> num * 2 }
println doubleNum(3) // => 6
processThenPrint = { num, closure ->
num = closure(num); println "num is $num"
}
processThenPrint(3, doubleNum) // => num is 6
processThenPrint(10) { it / 2 } // => num is 5

...Closures...
DSLs 2010 - 72
©ASERT2006-2010
int myConst = 4
def multiplier = { number -> number * myConst }
assert multiplier(10) == 40
Closure other = { it + myConst }
assert other.call(10) == 14
def twice = { it * 2 } // anonymous functions
assert twice(10) == 20 // implemented as Closures
Name

...Closures...
DSLs 2010 - 73
©ASERT2006-2010
int myConst = 4
Code

...Closures...
DSLs 2010 - 74
©ASERT2006-2010
int myConst = 4
Parameter(s)
Default parameter

...Closures...
DSLs 2010 - 75
©ASERT2006-2010
int myConst = 4
Call closure
Alternative syntax

...Closures...
DSLs 2010 - 76
©ASERT2006-2010
int myConst = 4
Free variable

...Closures...
DSLs 2010 - 77
©ASERT2006-2010
int myConst = 4
Bound to environment/context when called

Closures in DSLs...
DSLs 2010 - 78
©ASERT2006-2010
import static java.util.Calendar.*
def cart1 = [
[qty: 3, unitPrice: 50.0, gift: true,
name: 'Groovy in Action Book'],
[qty: 1, unitPrice: 40.0, gift: false,
name: 'Grails in Action eBook'],
name: 'Avatar DVD']
]
def cart2 = [
name: 'Groovy in Action Book'],
[qty: 2, unitPrice: 30.0, gift: false,
name: 'Avatar 3D DVD']
]
// ...
Nothing special here.
Just a list of maps.

... Closures in DSLs...
DSLs 2010 - 79
©ASERT2006-2010
// ...
def noDiscount = { it.unitPrice * it.qty }
def tenPercentOffAll = { it.unitPrice * it.qty * 0.9 }
def tenPercentOffGifts = { it.with {
unitPrice * qty * (gift ? 0.9 : 1.0)
} }
def tenPercentOffOverForty = { it.with {
unitPrice * qty * (unitPrice > 40 ? 0.9 : 1.0)
} }
def tenPercentOffBooks = { it.with {
unitPrice * qty * (name.contains('Book') ? 0.9 : 1.0)
} }
def tenPercentOffDVDs = { it.with {
unitPrice * qty * (name.contains('DVD') ? 0.9 : 1.0)
} }
def buyThreeGetOneFree = { it.with {
unitPrice * (qty % 3 + 2 * qty.intdiv(3))
} }
// ...
Closure Name

... Closures in DSLs...
DSLs 2010 - 80
©ASERT2006-2010
// ...
def noDiscount = { it.unitPrice * it.qty }
def tenPercentOffAll = { it.unitPrice * it.qty * 0.9 }
def tenPercentOffGifts = { it.with {
unitPrice * qty * (gift ? 0.9 : 1.0)
} }
def tenPercentOffOverForty = { it.with {
unitPrice * qty * (unitPrice > 40 ? 0.9 : 1.0)
} }
def tenPercentOffBooks = { it.with {
unitPrice * qty * (name.contains('Book') ? 0.9 : 1.0)
} }
def tenPercentOffDVDs = { it.with {
unitPrice * qty * (name.contains('DVD') ? 0.9 : 1.0)
} }
def buyThreeGetOneFree = { it.with {
unitPrice * (qty % 3 + 2 * qty.intdiv(3))
} }
// ...
Closure Code

... Closures in DSLs
DSLs 2010 - 81
©ASERT2006-2010
// ...
def specials = [noDiscount, tenPercentOffAll,
tenPercentOffGifts, tenPercentOffOverForty,
tenPercentOffBooks, tenPercentOffDVDs,
buyThreeGetOneFree]
[
SUNDAY..SATURDAY,
[cart1, cart2]
].combinations().each { day, cart ->
printf "%d %2.2fn", day,
cart.sum(specials[day-1])
}
1 240.00
2 216.00
3 220.00
4 225.00
5 221.00
6 235.00
7 190.00
1 110.00
2 99.00
3 105.00
4 105.00
5 105.00
6 104.00
7 110.00

Operator Overloading Example
DSLs 2010 - 82
©ASERT2006-2010
BigDecimal a = new BigDecimal(3.5d);
BigDecimal b = new BigDecimal(4.0d);
assert a.multiply(b).compareTo(new BigDecimal(14.0d)) == 0;
assert a.multiply(b).equals(new BigDecimal(14.0d).setScale(1));
def c = 3.5, d = 4.0
assert c * d == 14.0
• Java
• Groovy

Groovy Lab Example
DSLs 2010 - 83
©ASERT2006-2010
// require GroovyLab
import static org.math.array.Matrix.*
import static org.math.plot.Plot.*
def A = rand(10,3) // random Matrix of 10 rows and 3 columns
def B = fill(10,3,1.0) // one Matrix of 10 rows and 3 columns
def C = A + B // support for matrix addition with "+" or "-"
def D = A - 2.0 // support for number addition with "+" or "-"
def E = A * B // support for matrix multiplication or division
def F = rand(3,3)
def G = F**(-1) // support for matrix power (with integers only)
println A // display Matrix content
plot("A",A,"SCATTER") // plot Matrix values as ScatterPlot
def M = rand(5,5) + id(5) // Eigenvalues decomposition
println "M=n" + M
println "V=n" + V(M)
println "D=n" + D(M)
println "M~n" + (V(M) * D(M) * V(M)**(-1))

©ASERT2006-2010
Better Control Structures: Switch Poker…
suits = 'SHDC'
ranks = '23456789TJQKA'
suit = { String card -> suits.indexOf(card[1]) }
rank = { String card -> ranks.indexOf(card[0]) }
rankSizes = { List cards ->
cards.groupBy(rank).collect{ k, v -> v.size() }.sort() }
rankValues = { List cards ->
cards.collect{ rank(it) }.sort() }
// ...
8C TS KC 9H 4S 7D 2S 5D 3S AC
hand1 hand2
println rankSizes(["7S", "7H", "2H", "7D", "AH"])
// => [1, 1, 3]
DSLs 2010 - 84

©ASERT2006-2010
…Better Control Structures: Switch Poker…
// ...
flush = { List cards -> cards.groupBy(suit).size() == 1 }
straight = { def v = rankValues(it); v == v[0]..v[0]+4 }
straightFlush = { List cards -> straight(cards) && flush(cards)
}
fourOfAKind = { List cards -> rankSizes(cards) == [1, 4] }
fullHouse = { List cards -> rankSizes(cards) == [2, 3] }
threeOfAKind = { List cards -> rankSizes(cards) == [1, 1, 3] }
twoPair = { List cards -> rankSizes(cards) == [1, 2, 2] }
pair = { List cards -> rankSizes(cards) == [1, 1, 1, 2] }
// ...
DSLs 2010 - 85

©ASERT2006-2010
… Better Control Structures: Switch Poker
// ...
def rankHand(List cards) {
switch (cards) {
case straightFlush : return 9
case fourOfAKind : return 8
case fullHouse : return 7
case flush : return 6
case straight : return 5
case threeOfAKind : return 4
case twoPair : return 3
case pair : return 2
default : return 1
}
}
// ...
DSLs 2010 - 86

Type Transformation Example
DSLs 2010 - 87
©ASERT2006-2010
class InventoryItem {
def weight, name
InventoryItem(Map m) {
this.weight = m.weight; this.name = m.name
}
InventoryItem(weight, name) {
this.weight = weight; this.name = name
}
InventoryItem(String s) {
s.find(/weight=(d*)/) { all, w -> this.weight = w }
s.find(/name=(.*)/) { all, n -> this.name = n }
}
}
def room = [:]
def gold = [weight:50, name:'Gold'] as InventoryItem
def emerald = [10, 'Emerald'] as InventoryItem
def dagger = ['weight=5, name=Dagger'] as InventoryItem
room.contents = [gold, emerald, dagger]
room.contents.each{ println it.dump() }

DSLs 2010 - 88
Groovy DSL Features
©ASERT2006-2010

Metaprogramming
• Runtime Metaprogramming
– Categories including DGM
– invokeMethod, methodMissing, getProperty
– GroovyInterceptable
– ExpandoMetaClass
DSLs 2010 - 89
©ASERT2006-2010

DSLs 2010 - 90
©ASERT2006-2010
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"
} } } }
• MarkupBuilder

...Builders…
DSLs 2010 - 91
©ASERT2006-2010
def colors = ['red','darkOrange','blue','darkGreen']
(0..3).each { index ->
star( cx: 50 + (index*110), cy: 50, or: 40, ir: 15,
borderColor: 'black', count: 2+index, fill: colors[index] )
star( cx: 50 + (index*110), cy: 140, or: 40, ir: 15,
borderColor: 'black‘, count: 7+index, fill: colors[index] )
}
• GraphicsBuilder

…Builders
new AntBuilder().with {
echo(file:'Temp.java', '''
class Temp {
System.out.println("Hello");
}
}
''')
javac(srcdir:'.', includes:'Temp.java', fork:'true')
java(classpath:'.', classname:'Temp', fork:'true')
echo('Done')
}
// =>
// [javac] Compiling 1 source file
// [java] Hello
// [echo] Done
©ASERT2006-2010
DSLs 2010 - 92

93
A builder for HR

DSLs 2010 - 94
©ASERT2006-2010
ExpandoMetaClass…
import static java.lang.Character.isUpperCase
String.metaClass.swapCase = {
delegate.collect { ch ->
isUpperCase(ch as char) ?
ch.toLowerCase() :
ch.toUpperCase()
}.join()
}
println new Date().toString().swapCase()
// => sUN nOV 09 17:30:06 est 2008
List.metaClass.sizeDoubled = {-> delegate.size() * 2 }
LinkedList list = []
list << 1
list << 2
assert 4 == list.sizeDoubled()

DSLs 2010 - 95
©ASERT2006-2010
…ExpandoMetaClass
class Person {
String name
}
class MortgageLender {
def borrowMoney() {
"buy house"
}
}
def lender = new MortgageLender()
Person.metaClass.buyHouse = lender.&borrowMoney
def p = new Person()
assert "buy house" == p.buyHouse()

Adding your own control structures
• Thread enhancement
DSLs 2010 - 96
ROCK!
. 25
. 33
. 34
. 35
. 36
.. 131
.. 134
.. 137
.. 138
.. 139
... 232
... 234
... 237
... 238
... 239
.... 334
.... 336
.... 337
.... 338
.... 339
import java.util.concurrent.locks.ReentrantLock
import static System.currentTimeMillis as now
def startTime = now()
ReentrantLock.metaClass.withLock = { critical ->
lock()
try { critical() }
finally { unlock() }
}
def lock = new ReentrantLock()
def worker = { threadNum ->
4.times { count ->
lock.withLock {
print " " * threadNum
print "." * (count + 1)
println " ${now() - startTime}"
}
Thread.sleep 100
}
}
5.times { Thread.start worker.curry(it) }
println "ROCK!"
Source: http://chrisbroadfoot.id.au/articles/2008/08/06/groovy-threads

EMC DSL…
DSLs 2010 - 97
©ASERT2006-2010

...EMC Neo4j DSL…
DSLs 2010 - 98
©ASERT2006-2010
@GrabResolver(name= 'neo4j-public-repo', root= 'http://m2.neo4j.org')
@Grab('org.neo4j:neo4j-kernel:1.1.1')
import org.neo4j.kernel.EmbeddedGraphDatabase
import org.neo4j.graphdb.*
// an enum helper
enum MyRelationships implements RelationshipType { knows }
// some optional syntactic sugar using EMC DSL
Node.metaClass {
propertyMissing { String name, val ->
delegate.setProperty(name, val) }
propertyMissing { String name -> delegate.getProperty(name) }
methodMissing { String name, args ->
delegate.createRelationshipTo(args[0], MyRelationships."$name") }
}
Relationship.metaClass {
propertyMissing { String name, val ->
delegate.setProperty(name, val) }
propertyMissing { String name -> delegate.getProperty(name) }
}
// ...

…EMC Neo4j DSL
DSLs 2010 - 99
©ASERT2006-2010
// ...
def graphDb = new EmbeddedGraphDatabase("graphdb")
def tx = graphDb.beginTx()
def firstNode, secondNode, relationship
try {
firstNode = graphDb.createNode()
secondNode = graphDb.createNode()
relationship = firstNode.knows(secondNode)
firstNode.message = "Hello,"
secondNode.message = "world!"
relationship.message = "brave Neo4j"
tx.success()
} finally {
tx.finish()
println "$firstNode.message $relationship.message $secondNode.message"
// => Hello, brave Neo4j world!
graphDb.shutdown()
}

Game example...
DSLs 2010 - 100
©ASERT2006-2010
// Trying out the game DSL idea by Sten Anderson from:
// http://blogs.citytechinc.com/sanderson/?p=92
class GameUtils {
static VOWELS = ['a', 'e', 'i', 'o', 'u']
static listItems(things) {
def result = ''
things.eachWithIndex{ thing, index ->
if (index > 0) {
if (index == things.size() - 1) result += ' and '
else if (index < things.size() - 1) result += ', '
}
result += "${thing.toLowerCase()[0] in VOWELS ? 'an' : 'a'} $thing
}
result ?: 'nothing'
}
}
import static GameUtils.*
...

...Game example...
DSLs 2010 - 101
©ASERT2006-2010
...
class Room {
def description
def contents = []
}
...

...Game example...
DSLs 2010 - 102
©ASERT2006-2010
...
class Player {
def currentRoom
def inventory = []
void look() {
println "You are in ${currentRoom?.description?:'the void'}
which contains ${listItems(currentRoom?.contents)}"
}
void inv() {
println "You are holding ${listItems(inventory)}"
}
void take(item) {
if (currentRoom?.contents?.remove(item)) {
inventory << item
println "You took the $item"
} else {
println "I see no $item here"
}
}
...

...Game example...
DSLs 2010 - 103
©ASERT2006-2010
...
void drop(item) {
if (inventory?.remove(item)) {
currentRoom?.contents << item
println "You dropped the $item"
} else {
println "You don't have the $item"
}
}
def propertyMissing(String name) {
if (metaClass.respondsTo(this, name)) {
this."$name"()
}
name
}
}
...

...Game example...
DSLs 2010 - 104
©ASERT2006-2010
...
Room plainRoom = new Room(description:'a plain white room',
contents:['dagger', 'emerald', 'key'])
Player player = new Player(currentRoom:plainRoom)
player.with {
inv
look
take dagger
inv
look
take emerald
inv
look
take key
drop emerald
inv
look
}
assert player.inventory == ['dagger', 'key']
...

...Game example
DSLs 2010 - 105
©ASERT2006-2010
...
// now try some error conditions
plainRoom.description = null
player.with {
drop gold
take gold
drop emerald
take emerald
take emerald
look
}

GEP3 example...
DSLs 2010 - 106
©ASERT2006-2010
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

...GEP3 example...
DSLs 2010 - 107
©ASERT2006-2010
Object.metaClass.of =
{ delegate[0](delegate[1](it)) }
Object.metaClass.the =
{ clos -> [delegate[0], clos] }
show = [{ println it }]
please = { it }
please show the square_root of 100
// ==> 10.0

...GEP3 example...
DSLs 2010 - 108
©ASERT2006-2010
show = { println 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 …

...GEP3 example...
DSLs 2010 - 109
©ASERT2006-2010
// 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
// http://groovyconsole.appspot.com/edit/241001

...GEP3 example
DSLs 2010 - 110
©ASERT2006-2010
// source: http://d.hatena.ne.jp/uehaj/20100919/1284906117
// http://groovyconsole.appspot.com/edit/241001

Medical Prescription DSL…
DSLs 2010 - 111
©ASERT2006-2010
class Drug {
String name
String toString() { name }
}
class Measure {
Number number
String unit, units
String toString() { number == 1 ? "1 $unit" : "$number $units" }
}
class Quantity extends Measure {}
class Duration extends Measure {}
// ...
http://groovyconsole.appspot.com/script/240001 by glaforge/Mihai Cazacu

…Medical Prescription DSL…
DSLs 2010 - 112
©ASERT2006-2010
// ...
// ---- DSL implementation ------------------------------
Integer.metaClass.getHour = {-> 1.hours }
Integer.metaClass.getPill = {-> 1.pills }
Integer.metaClass.getHours = {-> new Duration(number: delegate,
unit: 'hour', units: 'hours') }
Integer.metaClass.getPills = {-> new Quantity(number: delegate,
unit: 'pill', units: 'pills') }
// use the script binding for storing new drugs available as variables
binding = new Binding() {
def getVariable(String drug) {
new Drug(name: drug)
}
}
take = {Quantity quantity ->
['of': {Drug drug ->
['after': {Duration duration ->
println "Take $quantity of $drug afer $duration"
}]
}]
}
// ...

…Medical Prescription DSL
DSLs 2010 - 113
©ASERT2006-2010
// ...
// ---- DSL -------------------------------
take 2.pills of chloroquinine after 6.hours
http://groovyconsole.appspot.com/script/240001 by glaforge/Mihai Cazacu

Groovy DSL Features
DSLs 2010 - 114
©ASERT2006-2010
Transformation

AST Transformations
• With metaprogramming, Groovy‟s able to
modify the behaviour of programs... at
runtime
• AST Transformations provide a compile-
time approach to modify programs
– 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 & local
DSLs 2010 - 115

Better Design Patterns: Immutable...
• Java Immutable Class
– As per Joshua Bloch
Effective Java
DSLs 2010 - 116
©ASERT2006-2010
public final class Punter {
private final String first;
private final String last;
return first;
}
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 Punter(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;
Punter other = (Punter) 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 "Punter(first:" + first
+ ", last:" + last + ")";
}
}

...Better Design Patterns: Immutable...
• Java Immutable Class
– As per Joshua Bloch
Effective Java
DSLs 2010 - 117
©ASERT2006-2010
public final class Punter {
private final String first;
private final String last;
return first;
}
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 Punter(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;
Punter other = (Punter) 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 "Punter(first:" + first
+ ", last:" + last + ")";
}
}
boilerplate

...Better Design Patterns: Immutable
DSLs 2010 - 118
©ASERT2006-2010
@Immutable class Punter {
String first, last
}

Spock
DSLs 2010 - 119
©ASERT2006-2010
def "length of Spock's & his friends' names"() {
expect:
name.size() == length
where:
name | length
"Spock" | 5
"Kirk" | 4
"Scotty" | 6
}

AST Builder
• Numerous approaches, still evolving.
“From code” approach:
• Produces:
def result = new AstBuilder().buildFromCode {
println "Hello World"
}
BlockStatement
-> ReturnStatement
-> MethodCallExpression
-> VariableExpression("this")
-> ConstantExpression("println")
-> ArgumentListExpression
-> ConstantExpression("Hello World")
DSLs 2010 - 120

©ASERT2006-2010
EasyB…
narrative 'segment flown', {
as_a 'frequent flyer'
i_want 'to accrue rewards points for every segment I fly'
so_that 'I can receive free flights for my dedication to the airline'
}
given 'a frequent flyer with a rewards balance of 1500 points'
when 'that flyer completes a segment worth 500 points'
then 'that flyer has a new rewards balance of 2000 points'
}
given 'a frequent flyer with a rewards balance of 1500 points', {
flyer = new FrequentFlyer(1500)
}
when 'that flyer completes a segment worth 500 points', {
flyer.fly(new Segment(500))
}
then 'that flyer has a new rewards balance of 2000 points', {
flyer.pointsBalance.shouldBe 2000
}
}
DSLs 2010 - 121

©ASERT2006-2010
…EasyB
examples "The number #{number}' should be converted to #{romanNumerals}", {
number = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
romanNumerals = ["I", "II", "III", "IV", "V",
"VI", "VII", "VIII", "IX", "X"]
}
scenario "Converting #number into the roman numeral #romanNumerals", {
given "the number #number", {
theNumber = number
}
when "the system converts this number to the roman numeral equivalent", {
theConvertedNumber = RomanNumerals.fromInteger(theNumber)
}
then "the result should be #romanNumerals", {
theConvertedNumber.shouldBe romanNumerals
}
}
DSLs 2010 - 122
Source: http://www.wakaleo.com/blog/285-example-driven-testing-with-easyb

EasyB Preprocessing...
• EasyB supports either of these:
• But we would like this:
given ("some data") {
println '... setting expectations'
}
Source: http://hamletdarcy.blogspot.com/2010/02/groovy-antlr-plugins-for-better-dsls.html
given "some data", {
}
given "some data" {
}
DSLs 2010 - 123
But also consider Command Expressions (GEP-3) for Groovy1.8+.

...EasyB Preprocessing...
String addCommas(text) {
def pattern =
~/(.*)(given|when|then) "([^"]*(.[^"]*)*)" {(.*)/
def replacement = /$1$2 "$3", {$4/
(text =~ pattern).replaceAll(replacement)
}
DSLs 2010 - 124
Adds the comma in where required before Groovy sees it.

...EasyB Preprocessing
class SourceModifierParserPlugin extends AntlrParserPlugin {
Reduction parseCST(SourceUnit sourceUnit, Reader reader)
throws CompilationFailedException {
def text = addCommas(reader.text)
StringReader stringReader = new StringReader(text)
super.parseCST(sourceUnit, stringReader)
}
}
def parserPluginFactory = new ParserPluginFactory() {
ParserPlugin createParserPlugin() {
new SourceModifierParserPlugin()
}
}
def conf = new CompilerConfiguration(pluginFactory: parserPluginFactory)
def binding = ...
def shell = new GroovyShell(binding, conf)
DSLs 2010 - 125
But use with restraint as error messages will be with
respect to converted source code not original.

GParsec...
• Miniature parsers
• Parser Combinators
def isLetter = { ch -> return Character.isLetter(ch) }
def isDigit = { ch -> return Character.isDigit(ch) }
def letter = satisfyC(isLetter)
def digit = satisfyC(isDigit)
def letterAndDigit = seqC(letter, digit)
assert letterAndDigit('a123###') == ['a', '1']
def identifier = seqC(identifierStart,
noneOrMoreC(identifierRest))
DSLs 2010 - 126

...GParsec...
• BNF
• Groovy definitions
variableDeclarator :
identifier ( '=' expression )?
variableDefinitions :
variableDeclarator ( ',' variableDeclarator)*
def variableDeclarator =
seqC(identifier, optionalC(seqC(assign, expression)))
def variableDefinitions =
seqC(variableDeclarator,
noneOrMoreC(seqC(comma, variableDeclarator)))
DSLs 2010 - 127

...GParsec
• satisfyC: combinator consumes a single input when its
predicate succeeds
• altC (alt3C, altCs): is the choice combinator. Given two
parsers it only looks at its second alternative if the first has
not consumed any input - regardless of the final value
• seqC (seq3C, seqCs): is the sequencing combinator. It runs
two parsers in succession and if successful, returns the result
of the two parsers
• noneOrMoreC, oneOrMoreC: applies a parser zero or more
times to an input stream. The result from each application of
the parser are returned in a list
• optionalC: The combinator optionalC may succeed in
parsing some input. It always returns success.
DSLs 2010 - 128

Using External Parsers
DSLs 2010 - 129
©ASERT2006-2010
import static com.mdimension.jchronic.Chronic.parse
def span = parse("tomorrow at 5pm")
println span.endCalendar.format('yyyy-MM-dd HH:mm')
// => 2010-05-19 17:00

Topics
• Introduction
A Week In The Life Of DSL INC
• Summary
• More Info
DSLs 2010 - 130
©ASERT2006-2010

MONDAY
DSLs 2010 - 131
©ASERT2006-2010

Currency DSL…
DSLs 2010 - 132
©ASERT2006-2010
From: customer@acme.org
To: Guillaume
Subject: Project Request
Dear Guillaume,
We would like a DSL for capturing currency expressions.
Just US currency to start with.
Thanks, Happy Customer

…Currency DSL...
DSLs 2010 - 133
©ASERT2006-2010
enum Coin {
penny(1), nickel(5), dime(10), quarter(25)
Coin(int value) { this.value = value }
int value
}
import static Coin.*
assert 2 * quarter.value +
1 * nickel.value +
2 * penny.value == 57

…Currency DSL…
DSLs 2010 - 134
©ASERT2006-2010
To: Guillaume
Dear Guillaume,
That works fairly well but can we get rid of the
‘.value’ part of those expressions. They are confusing
our users.

...Currency DSL...
DSLs 2010 - 135
©ASERT2006-2010
class CoinMath {
static multiply(Integer self, Coin c) {
self * c.value
}
}
use (CoinMath) {
assert 2 * quarter +
1 * nickel +
2 * penny == 57
}
// EMC equivalent
Integer.metaClass.multiply = {
Coin c -> delegate * c.value
}
assert 2 * quarter + 1 * nickel + 2 * penny == 57

…Currency DSL…
DSLs 2010 - 136
©ASERT2006-2010
To: Guillaume
Dear Guillaume,
Much better but our users are sometimes using
plural as well as singular expressions. Is there
anything that you can do about that?

... Currency DSL
DSLs 2010 - 137
©ASERT2006-2010
class CoinValues {
static get(Integer self, String name) {
self * Coin."${singular(name)}".value
}
static singular(String val) {
val.endsWith('ies') ? val[0..-4] + 'y' : val.endsWith('s') ? val[0..-2] : val
}
}
use (CoinValues) {
assert 2.quarters + 1.nickel + 2.pennies == 57
}
// EMC equivalent
Integer.metaClass.getProperty = { String name ->
def mp = Integer.metaClass.getMetaProperty(name)
if (mp) return mp.getProperty(delegate)
def singular = name.endsWith('ies') ? name[0..-4] + 'y' :
name.endsWith('s') ? name[0..-2] : name
delegate * Coin."$singular".value
}
assert 2.quarters + 1.nickel + 2.pennies == 57

TUESDAY
DSLs 2010 - 138
©ASERT2006-2010
http://www.google.com/imgres?imgurl=http://i733.photobucket.com/albums/ww336/snake1953/Day_of_Week/Tue/HappyTuesda

Business logic DSL…
DSLs 2010 - 139
©ASERT2006-2010
To: Paul King
Dear Paul,
Could you please create us a small DSL for capturing
our business rules. We are thinking of something like:
price = 3
quantity = 10
total = price * quantity
Perhaps also an ability to check values:
assert total == 30
P.S. Will send a couple of more details in a follow-up email but
please consider the requirements as being pretty much locked down.

…Business logic DSL…
• Options
– Embedded Groovy
– Regex parser
– Antlr parser
– Split / StringTokenizer
– Parser combinators
• … Many options, details not important …
DSLs 2010 - 140
©ASERT2006-2010

… Business logic DSL …
DSLs 2010 - 141
©ASERT2006-2010
To: Paul King
Date: Mid morning
Dear Paul,
We were thinking a bit more about it, and it would be good to have
just a few more features. Hopefully, they won’t have much impact
on your existing design and can be added very quickly. It isn’t
much, just the ability to have IF, THEN, ELSE like structures, oh
yeah and the ability to have loops, and store stuff in files and
get stuff from databases and web services if we need.
P.S. It would be great if you can be finished by this afternoon.
We have a customer who would like this feature RSN. Thanks.

DSLs 2010 - 142
©ASERT2006-2010
def shell = new GroovyShell()
shell.evaluate('''
price = 3
quantity = 10
assert total == 30
''')

DSLs 2010 - 143
©ASERT2006-2010
To: Paul King
Date: This afternoon
Dear Paul,
We were really happy with the DSL engine you provided us with
but people started importing all sorts of classes. Can you stop
them from doing that? Maybe just java.lang.Math only. Also we
decided we don’t like ‚while‛ loops anymore. Leave you to it.
P.S. Have a beer and crab dinner for me at the conference. Bye.

DSLs 2010 - 144
©ASERT2006-2010
class CustomerShell {
Object evaluate(String text) {
try {
def loader = new CustomerClassLoader()
def clazz = loader.parseClass(text)
def script = clazz.newInstance()
return script.run()
} catch (...) { ... }
}
}
class CustomerClassLoader extends GroovyClassLoader {
def createCompilationUnit(CompilerConfiguration config, CodeSource codeSource) {
CompilationUnit cu = super.createCompilationUnit(config, codeSource)
cu.addPhaseOperation(new CustomerFilteringNodeOperation(), Phases.SEMANTIC_ANALYSIS)
return cu
}
}
private class CustomerFilteringNodeOperation extends PrimaryClassNodeOperation {
// ...
private static final allowedStaticImports = [Math].asImmutable()
void visitStaticMethodCallExpression(StaticMethodCallExpression smce) {
if (!allowedStaticImports.contains(smce.ownerType.getTypeClass())) {
throw new SecurityException("Static method call expressions forbidden in acme shell.")
}
}
void visitWhileLoop(WhileStatement whileStatement) {
throw new SecurityException("While statements forbidden in acme shell.")
}
// ...
}
Please also see the ArithmeticShell which is included under examples in the Groovy distribution

… Business logic DSL
DSLs 2010 - 145
©ASERT2006-2010
def shell = new CustomerShell()
shell.evaluate('''
price = 3
quantity = 10
assert total == 30
''')

Stock Exchange Order DSL…
DSLs 2010 - 147
©ASERT2006-2010
Example inspired from DSLs in Action: http://www.manning.com/ghosh/
From: customer@finance-broker.org
To: Guillaume
Date: Wednesday morning
Dear Guillaume,
For our order processing system we have a need to capture client
orders using a DSL. An order includes the name of the security to
be transacted (buy or sell) as well as quantity and unit price details
to specify any constraint that the counterparty would like to impose
on the price of transaction.

… Stock Exchange Order DSL…
DSLs 2010 - 148
©ASERT2006-2010
// ----- Implementation of the Fluent API -----
enum Action { Buy, Sell }
class Order {
def security
def quantity, limitPrice
boolean allOrNone
def valueCalculation
Action action
def buy(Integer quantity, String security) {
this.quantity = quantity
this.security = security
this.action = Action.Buy
return this
}
def sell(Integer quantity, String security) {
this.quantity = quantity
this.security = security
this.action = Action.Sell
return this
}
def limitPrice(Integer limit) {
this.limitPrice = limit; return this
}
def allOrNone(boolean allOrNone) {
this.allOrNone = allOrNone; return this
}
def valueAs(Closure valueCalculation) {
this.valueCalculation = valueCalculation; return this
}
String toString() {
"$action $quantity shares of $security at valuation of ${valueCalculation(quantity, limitPrice)}"
}
}
println new Order()
.sell(150, "IBM")
.limitPrice(300)
.allOrNone(true)
.valueAs{ qty, unitPrice ->
qty * unitPrice - 100 }
println new Order()
.buy(200, "GOOG")
.limitPrice(200)
.allOrNone(true)
.valueAs{ qty, unitPrice ->
Sell 150 shares of IBM at valuation of 44900
Buy 200 shares of GOOG at valuation of 39500

…Stock Exchange Order DSL…
DSLs 2010 - 149
©ASERT2006-2010
To: Guillaume
Date: Wednesday morning
Dear Guillaume,
That version was great but can you make the
DSL a little more fluent. The brokers aren’t
programmers after all!

DSLs 2010 - 150
©ASERT2006-2010
class Order {
def security
def quantity
def limitPrice
def allOrNone
def value
def bs
def buy(securityQuantity, closure) {
bs = 'Bought'
buySell(securityQuantity, closure)
}
def sell(securityQuantity, closure) {
bs = 'Sold'
buySell(securityQuantity, closure)
}
private buySell(securityQuantity, closure) {
// multiple assignment
(security, quantity) = [securityQuantity.security, securityQuantity.quantity]
// better clone the closure to avoid multi-threading access issues
def c = closure.clone()
// delegate the method calls inside the closure to our methodMissing
c.delegationStrategy = Closure.DELEGATE_ONLY
c.delegate = this
def valuation = c()
println "$bs $quantity $security.name at valuation of $valuation"
}
// methods inside the closure will assign the Order properties
def methodMissing(String name, args) {
this."$name" = args[0]
}
...

DSLs 2010 - 151
©ASERT2006-2010
...
def getTo() { this }
def valueAs(closure) {
value = closure(quantity, limitPrice)
}
}
class Security {
String name
}
class Quantity {
Security security
Integer quantity
}
Integer.metaClass.getShares = { -> delegate }
Integer.metaClass.of = { new Quantity(security: it, quantity: delegate) }
class CustomBinding extends Binding {
def getVariable(String symbol) {
// create a new order each time
// for when you pass several orders
if (symbol == "newOrder")
new Order()
// otherwise, it's an instrument
// trick to avoid using strings: use IBM instead of 'IBM'
else
new Security(name: symbol)
}
}
// use the script binding for retrieving IBM, etc.
binding = new CustomBinding()
newOrder.to.buy(100.shares.of(IBM)) {
limitPrice 300
allOrNone true
valueAs { qty, unitPrice ->
}
newOrder.to.sell 200.shares.of(GOOG), {
limitPrice 200
allOrNone false
valueAs { qty, unitPrice ->
}

DSLs 2010 - 152
©ASERT2006-2010
To: Guillaume
Date: Wednesday lunch time
Dear Guillaume,
That version was great but can we simplify the
constraint to remove the parameters, i.e.: change
{ qty, unitPrice -> qty * unitPrice - 200 }
to this:
{ qty * unitPrice - 200 }

DSLs 2010 - 153
©ASERT2006-2010
class Order {
...
def allOrNone
def valueCalculation
def bs
...
private buySell(securityQuantity,
closure) {
...
valueCalculation = c()
// debug print resulting order
println toString()
return this
}
...
def valueAs(Closure wrapee) {
// in order to be able to define closures like { qty * unitPrice } without having
// to explicitly pass the parameters to the closure we can wrap the closure inside
// another one and that closure sets a delegate to the qty and unitPrice variables
def wrapped = { qty, unitPrice ->
def cloned = wrapee.clone()
cloned.resolveStrategy = Closure.DELEGATE_ONLY
cloned.delegate = [qty: qty, unitPrice: unitPrice]
cloned()
}
return wrapped
}
String toString() {
"$bs $quantity shares of $security.name and valuation of
${valueCalculation(quantity, limitPrice)}"
}
}
newOrder.to.buy(100.shares.of(IBM)) {
limitPrice 300
allOrNone true
valueAs { qty * unitPrice - 500 }
}
newOrder.to.sell 200.shares.of(GOOG), {
limitPrice 200
allOrNone false
valueAs { qty * unitPrice - 100 }
}

DSLs 2010 - 154
©ASERT2006-2010
To: Guillaume
Date: Wednesday afternoon
Dear Guillaume,
Fantastic! This is getting better all the time! But
can we get rid most of the ‘.’ and bracket symbols!

DSLs 2010 - 155
©ASERT2006-2010
// Characteristics of the order: "of GOOG {...}"
def of(SecurityAndCharacteristics secAndCharact) {
security = secAndCharact.security
def c = secAndCharact.characteristics.clone()
c.delegationStrategy = Closure.DELEGATE_ONLY
c.delegate = this
c()
// debug print of the resulting order
println toString()
return this
}
// Valuation closure: "of { qty, unitPrice -> ... }"
def of(Closure valueCalculation) {
// in order to be able to define closures like { qty * unitPrice }
// without having to explicitly pass the parameters to the closure
// we can wrap the closure inside another one
// and that closure sets a delegate to the qty and unitPrice variables
def wrapped = { qty, unitPrice ->
def cloned = valueCalculation.clone()
cloned.resolveStrategy = Closure.DELEGATE_ONLY
cloned.delegate = [qty: qty, unitPrice: unitPrice]
cloned()
}
return wrapped
}
String toString() {
"$action $quantity shares of $security.name at limit price of $limitPrice"
}
}
// ...
http://groovyconsole.appspot.com/script/226001 by glaforge

DSLs 2010 - 156
©ASERT2006-2010
// ...
class Security {
String name
}
class SecurityAndCharacteristics {
Security security
Closure characteristics
}
class CustomBinding extends Binding {
def getVariable(String word) {
// return System.out when the script requests to write to 'out'
if (word == "out") System.out
// don't thrown an exception and return null
// when a silent sentence word is used,
// like "to" and "the" in our DSL
null
}
}
// Script helper method for "GOOG {}", "VMW {}", etc.
def methodMissing(String name, args) {
new SecurityAndCharacteristics(
security: new Security(name: name),
characteristics: args[0]
)
}
// Script helper method to make "order to" silent
// by just creating our current order
def order(to) { new Order() }
// use the script binding for silent sentence words like "to", "the"
binding = new CustomBinding()
// syntax for 200.shares
Integer.metaClass.getShares = { -> delegate }

DSLs 2010 - 157
©ASERT2006-2010
// ---- Stock exchange orders DSL ----
order to buy 200.shares of GOOG {
limitPrice 500
allOrNone false
at the value of { qty * unitPrice - 100 }
}
order to sell 150.shares of VMW {
limitPrice 80
allOrNone true
at the value of { qty * unitPrice }
}
http://groovyconsole.appspot.com/script/226001 by glaforge

…Stock Exchange Order DSL
DSLs 2010 - 158
©ASERT2006-2010
To: Guillaume
Date: Wednesday evening
Dear Guillaume,
Brilliant! Even our CEO could write orders!

THURSDAY
DSLs 2010 - 159
©ASERT2006-2010
http://t1.gstatic.com/images?q=tbn:_VBloEP8YC-6IM:http://msp248.photobucket.com/albums/gg171/ingrid2002/TextPL252028

Einstein‟s Riddle DSL …
DSLs 2010 - 160
©ASERT2006-2010
To: Paul King
Date: Early morning
Dear Paul,
We would like a DSL for capturing our business rules.
Our business rules are captured in the form of logic clauses.
They are very much like those found in Einstein’s riddle.

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 below mentions brands of cigarette, such
as Kools, that did not exist during Carroll's lifetime or
Einstein's boyhood
DSLs 2010 - 161
©ASERT2006-2010

…Einstein‟s Riddle
DSLs 2010 - 162
©ASERT2006-2010
• 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
©ASERT2006-2010
% 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)|_]).
% The Dane drinks tea
hint3([(dane,_,tea,_,_)|_]).
% The Green house is on the left of the White house
hint4([(_,green,_,_,_),(_,white,_,_,_)|_]).
% The owner of the Green house drinks coffee.
hint5([(_,green,coffee,_,_)|_]).
...
DSLs 2010 - 163

DSLs 2010 - 164
©ASERT2006-2010
To: Paul King
Date: Early morning
Dear Paul,
Thanks for your Prolog solution but we don’t have
Prolog installed. Do you have a version that runs
on the JVM?

Einstein‟s Riddle : Polyglot
©ASERT2006-2010
@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
DSLs 2010 - 165

DSLs 2010 - 166
©ASERT2006-2010
To: Paul King
Date: Early morning
Dear Paul,
Thanks for that version but in terms of maintaining
the rules, we would like a more fluent expression
of the rules rather than Prolog? Any thoughts?

Einstein‟s Riddle : Polyglot w/ DSL…
©ASERT2006-2010
// 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'
DSLs 2010 - 167
// 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…
©ASERT2006-2010
DSLs 2010 - 168
// 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++
}
...

©ASERT2006-2010
DSLs 2010 - 169
// 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]) } ]
}
}]}
]
}
...

©ASERT2006-2010
DSLs 2010 - 170
// 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 // alt’n8 end: 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

DSLs 2010 - 171
©ASERT2006-2010
To: Paul King
Date: Early morning
Dear Paul,
That’s great. We even get some code completion
When using an IDE. Is there anything more we can
do to get more completion?

©ASERT2006-2010
DSLs 2010 - 172
// now implement DSL in terms of helper methods
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:
DSLs 2010 - 173
©ASERT2006-2010
„house‟ is key for a Map and could be any value

…Einstein‟s Riddle : Polyglot w/ DSL
©ASERT2006-2010
DSLs 2010 - 174
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

DSLs 2010 - 175
©ASERT2006-2010
To: Paul King
Date: Early morning
Dear Paul,
That’s fantastic! But we have just started
standardizing on Choco as our logic solving
engine. I guess we need to start from scratch.
Let me know what you think.

Einstein‟s Riddle : Choco w/ DSL…
©ASERT2006-2010
DSLs 2010 - 176
@GrabResolver('http://www.emn.fr/z-info/choco-solver/mvn/repository/')
@Grab('choco:choco:2.1.1-SNAPSHOT')
import static choco.Choco.*
import choco.kernel.model.variables.integer.*
def m = new choco.cp.model.CPModel()
m.metaClass.plus = { m.addConstraint(it); m }
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]
smokes = 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)
smokes[i] = makeEnumVar("smoke$i", smokes)
drinks[i] = makeEnumVar("drink$i", drinks)
nations[i] = makeEnumVar("nation$i", nations)
}
...

…Einstein‟s Riddle : Choco w/ DSL…
©ASERT2006-2010
DSLs 2010 - 177
// define DSL (simplistic non-refactored version)
def neighbours(var1, val1, var2, val2) {
and(
ifOnlyIf(eq(var1[0], val1), eq(var2[1], val2)),
implies(eq(var1[1], val1), or(eq(var2[0], val2), eq(var2[2], val2))),
ifOnlyIf(eq(var1[4], val1), eq(var2[3], val2))
)
}
iff = { e1, c1, e2, c2 -> and(*(0..<num).collect{
ifOnlyIf(eq(e1[it], c1), eq(e2[it], c2))
}) }
...
// define the DSL in terms of DSL implementation
def ctx = [nations, n]
[
drinks:iff.curry(*ctx, drinks),
smokes:iff.curry(*ctx, smokes),
keeps:iff.curry(*ctx, pets),
rears:iff.curry(*ctx, pets),
owns:{ _the -> [first:{ house -> eq(nations[first], n)}] },
...

…Einstein‟s Riddle : Choco w/ DSL…
©ASERT2006-2010
DSLs 2010 - 178
// define rules
m += all pets are different
m += all colors are different
m += all smokes are different
m += all drinks are different
m += all nations are different
m += the man from the centre house drinks milk
m += the Norwegian owns the first house
m += the Dane drinks tea
m += the German smokes prince
m += the Swede keeps dogs // alternate ending: has a pet dog
m += the Brit has a red house // alternate ending: red abode
m += the owner of the green house drinks coffee
m += the owner of the yellow house smokes dunhill
m += the person known to smoke pallmall rears birds // alt end: keeps birds
m += the man known to smoke bluemaster drinks beer
m += the green house is on the left side of the white house
m += the man known to smoke blends lives next to the one who keeps cats
m += the man known to keep horses lives next to the man who smokes dunhill
m += the man known to smoke blends lives next to the one who drinks water
m += the Norwegian lives next to the blue house
...

…Einstein‟s Riddle : Choco w/ DSL
• Output:
DSLs 2010 - 179
©ASERT2006-2010
def pretty(s, c, arr, i) { c.values().find{
it.ordinal() == s.getVar(arr[i])?.value } }
// 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 ' smokes ' + pretty(s, Smoke, smokes, i)
print ' drinks ' + pretty(s, Drink, drinks, i)
println ' and lives in a ' + pretty(s, Color, colors, i) + ' house'
}
more = s.nextSolution()
}
Solving Einstein's Riddle:
The Norwegian has a pet cat smokes dunhill drinks water and lives in a yellow house
The Dane has a pet horse smokes blends drinks tea and lives in a blue house
The Brit has a pet bird smokes pallmall drinks milk and lives in a red house
The German has a pet fish smokes prince drinks coffee and lives in a green house
The Swede has a pet dog smokes bluemaster drinks beer and lives in a white house

FRIDAY
DSLs 2010 - 180
©ASERT2006-2010
http://t3.gstatic.com/images?q=tbn:mgkj1lXpQ2-uWM:http://i298.photobucket.com/albums/mm269/bearyjuicylicious/comments

Important business meetings all afternoon!
DSLs 2010 - 181
©ASERT2006-2010
http://www.flickr.com/photos/bobswanson/5093775403/sizes/l/in/pool-52240148330@N01/

Some Finishing Guidelines
• Language and program evolve together …
In the end your program will look as if the
language had been designed for it … you
end up with code which is clear, small,
and efficient.
– Paul Graham
• Don‟t think just about Coding up your DSL
– But also about its target audience, its evolution,
required tool support and its testability
DSLs 2010 - 183

Start small, with key concepts
Beware over-engineering!

Grow your language
progressively

Get your hands dirty
Play with the end-users

Let your DSL fly,
it‟s not yours, it‟s theirs!

Tight feedback loop
Iterative process

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

Further Info…
DSLs 2010 - 192
©ASERT2006-2010
• Compilers : Principles, Techniques,
and Tools/ Edition 2, Alfred Aho, Ravi
Sethi, Jeffrey Ullman, Monica Lam
• Practical API Design : Confessions of
a Java Framework Architect, Jaroslav
Tulach
• Language Implementation Patterns :
Create Your Own Domain-Specific and
General Programming Languages,
Terence Parr

…Further Info
DSLs 2010 - 193
©ASERT2006-2010
• A model-driven framework for domain
specific languages, Martin Karlsch
• Design Guidelines for Domain Specific
Languages, Gabor Karsai et al
• Program Comprehension for Domain-
Specific Languages, Pereira et al
• Diagrammatic Representations in Domain-
Specific Languages, Konstantinos Tourlas
• DSLs in Action, Debasish Ghosh
• Domain-Specific Languages, Martin Fowler
• DSLs in Boo : Domain Specific Languages
in .NET, Ayende Rahien

GinA 2ed “ReGinA” is coming!
DSLs 2010 - 194
Contains a
chapter on
DSLs!

groovy DSLs from beginner to expert

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