1. Practical Considerations
for DSLs in Ruby
Muness Alrubaie
muness@gmail.com
muness.blogspot.com
ThoughtWorks
www.thoughtworks.com

2. ?
Ask!

3. What are we going to
talk about?

4. Text
A limited form of language
suitable for a specific class of
problems.
Domain Specific Language?

5. Venti half-caf, extra hot, no whip
mocha
DSL Example

6. Route 66, swinging, easy on
the chorus, extra solo at the
coda, and a bump at the end.
Scattered, smothered,
covered.
More examples

7. ... languages are not so much a
means of expressing truth that has
already been established, but are a
means of discovering truth that
was previously unknown.
Their diversity is a diversity not of
sounds and signs but of ways of
looking at the world.
Why?

8. Declarative Programming

9. External vs. Internal

12. Consideration 1: Focused

13. Fluent Interfaces

14. Composing fluent
interfaces
• Named Parameters
calendar.add 'a conference call', :on => 'may
3', :at => '4 PM'
• Method Chaining
calendar.add('a conference call').on('May
3').at('4 PM')
• Nested Calls
calendar.add a('conference call').on('May
3').at('4 PM')

15. Consideration 2: End In Mind

16. Consideration 3: DRY

19. Consideration 4:
Be Context Sensitive

21. The fascinating thing is that, in my experience,
most well-written Ruby programs are already
a DSL, just by nature of Ruby’s syntax.
Symbols, blocks, optional parentheses around
parameters—these all go a long way toward
making Ruby programs read naturally.
Additionally, a well-designed application
encapsulates its problem domain, which also
just happens to be a good metric for
determining the effectiveness of a DSL. A DSL
can be thought of as (and many cases, really is)
an API for your application.

22. Consideration 5:
Evolve into a DSL

23. Considerations
• Focused
• Begin with the End in Mind
• Don’t repeat your context
• Take advantage of run-time context
• Evolve your implementation into DSL

24. Resources
• Martin Fowler on:
• Language Workbenches
• Internal DSL Style
• Fluent Interfaces
• Writing Domain Specific Languages, Jamis Buck
• Evolving an Embedded DSL in Java, Steve Freeman and Nat
Pryce
• Language Oriented Programming: The Next programming
Paradigm, Sergey Dmitriev
• Software Factories, Microsoft

25. ?
session
evaluations
Muness Alrubaie
muness@gmail.com
muness.blogspot.com
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