Type-safe DSLs

Type-safe DSLs
Using Xtext/TS, Xtend, Groovy and
other languages
Werner Keil

Eclipse DemoCamp Hamburg
14th June 2012

Our Goal

AVOIDING ARITHMETIC OR
TYPE ERRORS IN A DSL

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&A

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?
Real-Time Business
Systems Systems

Requirements

Specification

Aircraft Patient Insurance
control Management Management Implementation
systems Systems Systems

Deployment


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 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.


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 agency's 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 Offshore


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.


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 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 Example
Person 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);
}

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()

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
• HL7's extensions called ISO+


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


Healthcare DSL with Groovy

DEMO

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)

Result
Starting Cost: 23.75
Tip Percentage: 0.15
Tax Percentage: 0.07
29


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.


Scala and Fantom Examples

DEMO

Links

Eclipse – Project UOMo
http://www.eclipse.org/uomo/

Units of Measurement API
http://www.unitsofmeasurement.org

UCUM
http://www.unitsofmeasure.org

Links (2)

OpenHealth Project
http://www.openhealth.org

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

Jython
http://www.jython.org

Links (3)

Xtext
http://www.eclipse.org/xtext

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

Fantom
http://fantom.org/

Contact

werner@catmedia.us
or
uomo@catmedia.us

Twitter: @wernerkeil
Hashtag #EclipseUOMo

Type-safe DSLs

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