1. Construction Techniques for
Domain-Specific Languages
Brian Guthrie
bguthrie@thoughtworks.com
http://twitter.com/bguthrie

2. properties
http://www.flickr.com/photos/frozenchipmunk/52753779/

3. “a computer programming language of
limited expressiveness
focused on a particular domain.”

4. “a computer programming language of
limited expressiveness
focused on a particular domain.”

5. “a computer programming language of
limited expressiveness
focused on a particular domain.”

6. “a computer programming language of
limited expressiveness
focused on a particular domain.”
“iced quad venti (with whip) skinny caramel macchiato”

7. “a computer programming language of
limited expressiveness
focused on a particular domain.”
“iced quad venti (with whip) skinny caramel macchiato”

8. “a computer programming language of
limited expressiveness
focused on a particular domain.”

9. “a computer programming language of
limited expressiveness
focused on a particular domain.”

10. “a computer programming language of
limited expressiveness
focused on a particular domain.”

11. “a computer programming language of
limited expressiveness
focused on a particular domain.”

12. “a computer programming language of
limited expressiveness
focused on a particular domain.”

13. “a computer programming language of
limited expressiveness
focused on a particular domain.”

14. “a computer programming language of
limited expressiveness
focused on a particular domain.”

15. “a computer programming language of
limited expressiveness
focused on a particular domain.”
<target name="test" depends="compile" description="Runs tests">
<javac
destdir="${classes.dir}"
debug="true"
source="${javac.version}"
target="${javac.version}">
<classpath refid="build.classpath"/>
<src path="${test.dir}"/>
<include name="**/*.java"/>
</javac>
</target>

16. “a computer programming language of
limited expressiveness
focused on a particular domain.”
<target name="test" depends="compile" description="Runs tests">
<javac
destdir="${classes.dir}"
debug="true"
source="${javac.version}"
target="${javac.version}">
<classpath refid="build.classpath"/>
<src path="${test.dir}"/>
<include name="**/*.java"/>
</javac>
</target>

17. “a computer programming language of
limited expressiveness
focused on a particular domain.”
<target name="test" depends="compile" description="Runs tests">
<javac
destdir="${classes.dir}"
debug="true"
source="${javac.version}"
target="${javac.version}">
<classpath refid="build.classpath"/>
<src path="${test.dir}"/>
<include name="**/*.java"/>
</javac>
</target>

18. 2 flavors
internal external

19. 2 flavors
internal external

20. 2 flavors
internal external

21. API

22. expressiveness
implementation details

23. fluent interface

24. a behavior capable of
relaying
or
maintaining
the
instruction context
for a series of method calls

25. methods make little sense
out of context

26. [example]

28. a good candidate
source: http://lobobrowser.org/cobra/java-html-parser.jsp

29. forces
CHOICES
early and often

30. be
DECLARATIVE

31. be
accepting

32. every API is a conversation
http://www.flickr.com/photos/11739182@N03/1263985679/

33. with yourself

34. with your team members

35. with your business

36. patterns
http://www.flickr.com/photos/mukluk/477913951/

37. example one
method chaining | type transmogrification

38. example one
method chaining | type transmogrification
make modifier methods return the host
object so that multiple modifiers
can be invoked in a single expression.

39. example one
method chaining | type transmogrification

40. example one
method chaining | type transmogrification
transform types as needed as part
of a fluent interface call

41. start with the goal
http://www.flickr.com/photos/keylosa/184606430/

42. Calendar

46. Mocha

48. what does expects return?

49. mocha/mock.rb
(ArgumentIterator#each returns the Expectation-trust me)

50. mocha/expectation.rb

51. the finishing problem
when will it all end?

52. implied contract
type transformations are hidden from the caller
the system will arrive at some desired state

53. example two
nested closures | semantic model

54. example two
nested closures | semantic model

55. example two
nested closures | semantic model
express statement sub-
elements of a function call by putting them
into a closure in an argument

56. example two
nested closures | semantic model

57. example two
nested closures | semantic model
the domain model underpinning
the DSL

58. Awsymandias
look on my racks, oh ye mighty, and despair.
http://github.com/bguthrie/awsymandias
http://www.flickr.com/photos/stuckincustoms/197905054/

59. define an environment

60. persist metadata to S3

61. spin up in EC2

64. DSL is a wrapper for a
rich domain model
don’t corrupt it!

68. important
definition != domain model

69. domain model
dsl definition

70. A DSL is a language
parse its inputs!
keep your domain model clean!

72. example three
literal extension | string polishing

73. example three
literal extension | string polishing
add methods to program literals
“monkey patching”

74. example three
literal extension | string polishing
simple string substitutions to convert
nearly code to actual code

75. the problem

76. source: http://lobobrowser.org/cobra/java-html-parser.jsp

77. the goal

78. web page
to
object model

80. org.w3c.Node

81. org.w3c.Node java.util.List

82. groovy already extends
Node

83. DOMCategory

84. (brief digression)

87. shotgun approach to
open classes

88. “all willy-nilly”

89. http://www.flickr.com/photos/tenioman/2771903123/

90. irb

91. script/console (in rails)

93. back to Groovy...

94. use (DOMCategory) {
children(), attributes(),
Element text(), name(), parent(),
depthFirst(), breadthFirst()
NodeList size(), list(), text(), child
}

95. this is awesome!

96. and speaking of which...

97. we can do better!

101. search?

105. example four
literal extension | method chaining

108. literal extension at the
object level

109. jQuery objects
act like arrays

110. jQuery objects
are arrays

111. duck typing?
http://www.flickr.com/photos/martinlabar/694274715/

112. example five
method chaining andChaining andChaining

114. message chains

115. mimic: cloning is
expected and
encouraged

117. “iced quad venti (with whip) skinny caramel macchiato”

122. calories
http://www.flickr.com/photos/lifeontheedge/2077384723/
“the leaning tower of bacon”

125. http://www.flickr.com/photos/wili/214317898/
bringing
it all
back
home

126. a DSL is:
- an API
- a language
- a conversation

127. be
DECLARATIVE

128. know your audience

129. fluent interface

130. message chains

131. nested
function | closure

132. include  use  extend  eval

133. Brian Guthrie
bguthrie@thoughtworks.com
http://twitter.com/bguthrie
questions?