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Type-safe DSLs

Groovy founder Guillaume Laforge built on top of the Java standard proposal for type safe Units of Measurements, JSR-275 with his case study of a Domain-Specific Language for unit manipulations some while ago.
Based on Unit-API the successor to JSR-275, and its leading Open Source implementation Eclipse UOMo together with Xtext/TS we'll see, how a similar DSL for unit manipulations could be created with Xtext. As well as other languages including Groovy or Scala.

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Type-safe DSLs

  1. 1. Type-safe DSLsUsing Xtext/TS, Xtend, Groovy andother languages Werner Keil Eclipse DemoCamp Hamburg 14th June 2012
  2. 2. Our Goal AVOIDING ARITHMETIC OR TYPE ERRORS IN A DSL2 © 2007-2012 Creative Arts & Technologies
  3. 3. Overview• Introduction • What is a DSL? • Internal and External DSLS • Type-Safety• Units and Healthcare • Unit-API, UOMo • UCUM, HL7, Groovy used by Healthcare• Other Languages • Jython/WLST • Xtext/Xbase/Xtend • Scala, Fantom, F#• Demo• Q&A3 © 2007-2012 Creative Arts & Technologies
  4. 4. Who am I?Werner Keil • Consultant – Coach • Creative Cosmopolitan • Open Source Evangelist • Software Architect • Java Godfather • … Twitter @wernerkeil4 © 2007-2012 Creative Arts & Technologies
  5. 5. What is a DSL?• A DSL is a computer language (specification, modeling, programming) tailored to a particular domain. But, what is a domain?• DSL examples: SQL, CSS, Sawzall (Google)• Gains in expressiveness and ease of use (the future could be end-user programming)• Gains in productivity• Reduced maintenance costs5 © 2007-2012 Creative Arts & Technologies
  6. 6. What is a Domain? Real-Time Business Systems Systems Requirements Specification Aircraft Patient Insurance control Management Management Implementation systems Systems Systems Deployment6 © 2007-2012 Creative Arts & Technologies
  7. 7. Internal Domain Specific Languages• These are languages built using the syntactic elements of the underlying language• In the case of Java, building a DSL using Java classes and methods• With other JVM-based languages, that’s usually similar, Java code generated in many cases7 © 2007-2012 Creative Arts & Technologies
  8. 8. External Domain Specific Languages• External DSLs • Written in a different language than the main (host) language of the application • Transformed into it using some form of compiler or interpreter• May include • XML configuration files • Plain text configuration files • Full-blown languages8 © 2007-2012 Creative Arts & Technologies
  9. 9. Type-Safety• Java does not have strongly typed primitive types (like e.g. Ada language).• For performance reasons most developer prefer primitive types over objects in their interface.• Primitives type arguments often lead to name clashes (methods with the same signature)9 © 2007-2012 Creative Arts & Technologies
  10. 10. What do these disasters have in common?• Patriot Missile The cause was an inaccurate calculation of the time since boot due to a computer arithmetic error.• Ariane 5 Explosion The floating point number which a value was converted from had a value greater than what would be represented by a 16 bit signed integer.10 © 2007-2012 Creative Arts & Technologies
  11. 11. What do these disasters have in common?• Gimli Glider (near disaster) Fuel loading was miscalculated through misunderstanding of the recently adopted Metric System, replacing the Imperial System• Mars Orbiter Preliminary findings indicate that one team used English units (e.g. inches, feet and pounds) while the other used metric units for a key spacecraft operation. • NASA lost a $125 million Mars orbiter because a Lockheed Martin engineering team used English units of measurement while the agencys team used the more conventional metric system for a key spacecraft operation • This also underlines the added risk when 3 rd party contractors are involved or projects are developed Offshore11 © 2007-2012 Creative Arts & Technologies
  12. 12. Unit Tests wouldn‘t find these… Despite their name• All previous example illustrate three categories of errors difficult to find through Unit Testing: • Interface Errors (e.g. millisecond/second, radian/degree, meters/feet). • Arithmetic Errors (e.g. overflow). • Conversion Errors.17 © 2007-2012 Creative Arts & Technologies
  13. 13. SQL Example with Errors StringBuilder sql = new StringBuilder(); sql.append("SELECT o.sum,(SELECT first_name,last_name"); sql.append(" FROM person p"); sql.append(" WHERE AS client"); sql.append(" FROM order o"); sql.append("WHERE = "+orderId); sql.append(" AND o.status_code IN (?,?)"); PreparedStatement stmt = conn.prepareStatement(sql.toString()); stmt.setString(1, "PAID"); //...19 © 2007-2012 Creative Arts & Technologies
  14. 14. Typesafe SQL Example Person p = new Person(); List<Tuple<String, Integer, Date>> rows = new QueryBuilder(datasource) .from(p) .where(gt(p.height, 170)) .select(, p.height, p.birthday) .list(); for (Tuple<String, Integer, Date> row : rows) { String name = row.v1; Integer height = row.v2; Date birthday = row.v3; System.out.println( name + " " + height + " " + birthday); }20 © 2007-2012 Creative Arts & Technologies
  15. 15. Unit-API | Operations Results with Same Dimension Different Dimension Binary Operations Binary Operations add(double) or (long) root(int) multiply(double) or (long) power(int) divide(double) or (long) multiply(Unit) compound(Unit) divide(Unit) Unary Operations inverse()
  16. 16. UOMo UCUM Unified Code for Units of Measure The Unified Code for Units of Measure is inspired by and heavily based on • ISO 2955-1983 • ANSI X3.50-1986 • HL7s extensions called ISO+25 © 2007-2012 Creative Arts & Technologies
  17. 17. HL7 DSL def mySegment = ... // assignment to another NK1 segment instance def group = message.PATIENT_RESULT(0).PATIENT group.NK1(0) = abc // syntax error! msg1.NK1(0) = mySegment // syntax error! msg1.NK1(0).from(mySegment) // works! def nk1 = message.PATIENT_RESULT(0).PATIENT.NK1(0) def otherNk1 = message.PATIENT_RESULT(0).PATIENT.NK1(0) nk1[4] = otherNk1[4] // copy address nk1[4][4] = otherNk1[4][4] // copy state or province only nk1[4][4].from(otherNk1[4][4])// equivalent nk1[4][4] = NY // set state or province directly26 © 2007-2012 Creative Arts & Technologies
  18. 18. Healthcare DSL with Groovy DEMO
  19. 19. Jython /** * Java calculator class that contains two simple methods */ public class Calculator { public Calculator(){ } public double calculateTip(double cost, double tipPercentage) { return cost * tipPercentage; } public double calculateTax(double cost, double taxPercentage) { return cost * taxPercentage; } }28 © 2007-2012 Creative Arts & Technologies
  20. 20. Jython (2) import Calculator from java.lang import Math class JythonCalc(Calculator): def __init__(self): pass def calculateTotal(self, cost, tip, tax): return cost + self.calculateTip(tip) + self.calculateTax(tax) if __name__ == "__main__": calc = JythonCalc() cost = 23.75 tip = .15 tax = .07 print "Starting Cost: ", cost print "Tip Percentage: ", tip print "Tax Percentage: ", tax print Math.round(calc.calculateTotal(cost, tip, tax))29 © 2007-2012 Creative Arts & Technologies
  21. 21. Jython (3) Result Starting Cost: 23.75 Tip Percentage: 0.15 Tax Percentage: 0.07 2930 © 2007-2012 Creative Arts & Technologies
  22. 22. Xtext Examples DEMO
  23. 23. Scala, Fantom, F#• Scala • Functional programming language. Type-safe, as the company driving it was called. • Very popular for DSLs• Fantom • Functional programming language • Units of Measurement support built in. • Runs on both JVM and CLR• F# • Functional programming language • Units of Measurement support built in.33 © 2007-2012 Creative Arts & Technologies
  24. 24. Scala and Fantom Examples DEMO
  25. 25. Links Eclipse – Project UOMo Units of Measurement API UCUM
  26. 26. Links (2) OpenHealth Project Groovy DSL Example specific-language-unit- Jython
  27. 27. Links (3) Xtext Scala DSLs Fantom
  28. 28. Let‘s talkQ&A
  29. 29. Contact or Twitter: @wernerkeil Hashtag #EclipseUOMo