Domain Specific Languages
Design Patterns and Methodologies
Lakshan Perera (lakshan@web2media.net)
Faculty of Information Technology
University of Moratuwa

“Our understanding of the nature of
language and the mental processes
and structures that underlies its use
and acquisition”
Noam Chomsky
Cartesian Linguistics

What is
Domain Specific Language(DSL) ?

“(DSL) is a computer language that's
targeted to a particular kind of problem,
rather than a general purpose language
that's aimed at any kind of software
problem.”
Martin Fowler

th
4 Generation of
Programming
Languages

Evolution
➣ APT (1957 – 1958)
➣ COBOL, FORTRAN and PERL
➣ Unix Mini-languages (yacc, lex, make)
➣ Lisp (Bottom-up design)

Advantages of using DSL

Direct Involvement
of Domain Expert

Improved Productivity

Runtime Efficiency

Considerations
➣ Cost
➣ Language of choice
➣ Complexity of Design
➣ Scope

Developing a DSL

Domain Analysis

Designing DSL
➣ Piggyback
➣ Language Extension
➣ Language Specialization

Implementing DSL

Internal vs External

External DSL
➣ Interpreter
➣ Compiler/application generator
➣ Preprocessor
➣ Extensible compiler or preprocessor

Internal DSL
➣ Method Chaining
➣ Expression Builder
➣ Closures
➣ Literal Collections
➣ Object Scoping
➣ Open Classes

Real World Examples

SELECT books .title, count(*) AS
Authors
FROM books
JOIN book_authors ON books .is
bn = book_authors .is bn
GROUP BY books .title;

class Category < ActiveRecord::Base
has_many :articles
validates_presence_of :name
validates_uniqueness_of :name
def url_param
self.name.downcase.gsub(/\\s/,'_')
end
end

employee John Doe
compensate 500 dollars for each deal
closed in the past 30 days
compensate 100 dollars for each active deal
that closed more than 365 days ago
compensate 5 percent of gros s profits if
gross profits are greater than 1,000,000
dollars
compensate 3 percent of gros s profits if
gross profits are greater than 2,000,000
dollars

Future
(Everyone is a programmer)

Questions?