type-safe dsls

Type-safe DSLs

Using Xtext/TS, Xtend, Groovy and other languages

Werner Keil

Eclipse DemoCamp Hamburg

14th June 2012

AVOIDING ARITHMETIC OR TYPE ERRORS IN A DSL

Our Goal

2 © 2007-2012 Creative Arts & Technologies

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

Who am I?


Werner Keil

• Consultant – Coach

• Creative Cosmopolitan

• Open Source Evangelist

• Software Architect

• Java Godfather

• …

Twitter @wernerkeil

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 costs


What is a Domain?


Implementation

Specification

Requirements

Deployment

Business

SystemsReal-Time

Systems

Aircraft

control

systems

Patient Management

Systems

Insurance

Management

Systems

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 cases


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 languages


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)


What do these disasters have in common?•Patriot MissileThe cause was an inaccurate calculation of the time since boot due to a computer arithmetic error.

•Ariane 5 ExplosionThe floating point number which a value was converted from had a value greater than what would be represented by a 16 bit signed integer.


• 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 agency's team used the more conventional metric system for a key spacecraft operation

• This also underlines the added risk when 3rd party contractors are involved or projects are developed Offshore

What do these disasters have in common?


Unit Tests wouldn‘t find these…

•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.

Despite their name


SQL Example with ErrorsStringBuilder sql = new StringBuilder();

sql.append("SELECT o.sum,(SELECT first_name,last_name");

sql.append(" FROM person p");

sql.append(" WHERE o.person_id=p.id) AS client");

sql.append(" FROM order o");

sql.append("WHERE o.id = "+orderId);

sql.append(" AND o.status_code IN (?,?)");

PreparedStatement stmt = conn.prepareStatement(sql.toString());

stmt.setString(1, "PAID");

//...


Typesafe SQL ExamplePerson p = new Person();

List<Tuple<String, Integer, Date>> rows =

new QueryBuilder(datasource)

.from(p)

.where(gt(p.height, 170))

.select(p.name, 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);

}


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()

Unit-API | Operations

Unified Code for Units of Measure

The Unified Code for Units of Measure is inspired byand heavily based on

• ISO 2955-1983

• ANSI X3.50-1986

• HL7's extensions called ISO+

UOMo UCUM


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 directly

DEMO

Healthcare DSL with Groovy

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;

}

}

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))

Jython (3)


Starting Cost: 23.75

Tip Percentage: 0.15

Tax Percentage: 0.07

29

Result

DEMO

Xtext Examples

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.


DEMO

Scala and Fantom Examples

Eclipse – Project UOMo

http://www.eclipse.org/uomo/

Units of Measurement API

http://www.unitsofmeasurement.org

UCUM

http://www.unitsofmeasure.org

Links

http://www.eclipse.org/uomo/

http://www.unitsofmeasurement.org/

http://www.unitsofmeasure.org/

OpenHealth Project

http://www.openhealth.org

Groovy DSL Example

http://groovy.dzone.com/news/domain-specific-language-unit-

Jython

http://www.jython.org

Links (2)

http://www.openhealth.org/



http://www.jython.org/

Xtext

http://www.eclipse.org/xtext

Scala DSLs

http://www.scala-lang.org/node/1403

Fantom

http://fantom.org/

Links (3)

http://www.eclipse.org/xtext

http://www.scala-lang.org/node/1403

http://fantom.org/

Q & ALet‘s talk

Contact

[email protected]

or

[email protected]

Twitter: @wernerkeil

Hashtag #EclipseUOMo

mailto:[email protected]

mailto:[email protected]

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