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SimJ Programming Language
BUILD ON THE POLYGLOT COMPILER
FRAMEWORK
MIHAL BRUMBULLI
7th Workshop “SEERE”
Montenegro-Risan 9-14 September 2007
Introduction
2
 Goal: “Build a new programming language”

For beginners
Redable & Easy code
 No complexity
 Basic functionality (found in beginners programming text books)


For compiler design
Basic functionality (not too complex)
 Most important data types
 Very similiar to Java (not an exact copy of it)
 Implemented in a compiler framework

Polytechnic University of Tirana
M. Brumbulli
Polyglot Compiler Framework
3
 An extensible Java compiler toolkit designed for
experimentation with new language extensions.
 The base polyglot compiler is a mostly-complete Java
front end.


It parses, performs semantic checking on Java source code and
outputs Java source code.
Its power consists in doing so on other languages source codes.
 The AST is translated into a Java AST and the existing
code is output into a Java source file which can then be
compiled with javac.
Polytechnic University of Tirana
M. Brumbulli
Framework Architecture
4
Polytechnic University of Tirana
M. Brumbulli
Language Extensions
5
 An extension is a source-to-source compiler that
accepts a program written in a language extension
and translates it to Java source code.
 The first step in compilation is parsing input source
code to produce an AST.

Polyglot includes an extensible parser generator, PPG, which
allows the implementer to define the syntax of the language
extension as a set of changes to the base grammar for Java.
Polytechnic University of Tirana
M. Brumbulli
Language Extentions cont...
6
 The second step consist in a set of passes that
transform the produced AST in a JavaAST.


The pass scheduler selects passes to run over the AST of a
single source file in an order defined by the extension.
Each compilation pass, if successful, rewrites the AST,
producing a new AST that is the input to the next pass.
 Finally, a Java compiler such as javac is invoked to
compile the Java code to bytecode.
Polytechnic University of Tirana
M. Brumbulli
SimJ Language
7
 Is a simplified version of the Java programming
language.

Not just a reduced copy of Java (MiniJava).
 Simple Java like program structure.
 Not some simple, command like instructions (J0) .
 Two possible targets:
 Beginners with no experience in programming.
 Compiler construction.
Polytechnic University of Tirana
M. Brumbulli
SimJ Language cont...
8
 Classes, Methods, ...
 Data types
 boolean – true or false
 int – integers
 char – characters
 string – sequence of characters
 int[] – array of integers
 Control flow
 if else
 for
 while
 switch
Polytechnic University of Tirana
M. Brumbulli
SimJ vs Java
9
Java
public class A {
public static void main(String[] args) {
try {
BufferedReader reader = new
BufferedReader(new InputStreamReader
(System.in));
System.out.print(“Your name:”);
String name = reader.readLine();
System.out.print(“\nHello, ”+name+ “!”);
}
catch (IOException ioexeption) {
System.out.println(ioexeption);
}
}
}
Polytechnic University of Tirana
SimJ
class A {
main() {
print(“Your name:”);
string name = readLine();
print(“\nHello, ”+name+“!”);
}
}
M. Brumbulli
Implementation
10
 The design process of SimJ includes the following
tasks:

Syntactic differences between SimJ and Java are defined based
on the Java grammar:


Any new AST nodes that SimJ requires are defined based on
the existing Java nodes found in:



polyglot/ext/jl/parse/java12.cup.
polyglot.ast and polyglot.ext.jl.ast .
Semantic differences between SimJ and Java are defined.
Translation from SimJ to Java is defined. The translation
produces a legal Java program that can be compiled by javac.
Polytechnic University of Tirana
M. Brumbulli
Implementation cont...
11
 Resulting packages are:
 ext.simj.ast


ext.simj.extension


Type objects and typing judgments specific to SimJ.
ext.simj.visit


New extension and delegate objects specific to SimJ.
ext.simj.types


AST nodes specific to SimJ language.
Visitors specific to SimJ.
ext.simj.parse

The parser and lexer for the SimJ language.
Polytechnic University of Tirana
M. Brumbulli
Conclusions
12
 SimJ is a simple programming language that
improves the learning of programming basic
structures.

the existing approaches did not fully address the problem of a
simplified Java like structured language and that is not only a
reduced copy of it.
 Simplicity of SimJ is principally gained by hiding
some of the Java object-orientation syntax in the
usage of basic statements.

This improves the understandability of the code, making it less
confusing and definitely more easy to learn.
Polytechnic University of Tirana
M. Brumbulli
Conclusions cont...
13
 Polyglot Framework is an effective and easy way to
produce compilers for Java-like languages like SimJ.

It offers the possibility to generate a base skeleton for new
language extensions on witch we can add the desired
specifications.
 SimJ is a simplified version of the Java programming
language that is not only a reduced copy of it.


SimJ could be used by beginners that want to learn Java but
don’t know anything about programming.
It is also a good choice for learning compiler design because of
its well defined and easy to implement structure.
Polytechnic University of Tirana
M. Brumbulli
THANK YOU!
MIHAL BRUMBULLI