Java-centered Translator-based Multi-paradigm Software Development Environment

Xiaohong (Sophie) Wang
International Journal of Software Engineering (IJSE), Volume (3) : Issue (2) : 2012 32
Java-centered Translator-based Multi-paradigm
Software Development Environment
Xiaohong (Sophie) Wang xswang@salisbury.edu
Department of Mathematics and Computer Science
Salisbury University
Salisbury, MD 21801, USA
Abstract
This research explores the use of a translator-based multi-paradigm programming method to
develop high quality software. With Java as the target language, an integrated software
development environment is built to allow different parts of software implemented in Lisp, Prolog,
and Java respectively. Two open source translators named PrologCafe and Linj are used to
translate Prolog and Lisp program into Java classes. In the end, the generated Java classes are
compiled and linked into one executable program. To demonstrate the functionalities of this
integrated multi-paradigm environment, a calculator application is developed. Our study has
demonstrated that a centralized translator-based multi-paradigm software development
environment has great potential for improving software quality and the productivity of software
developers. The key to the successful adoption of this approach in large software development
depends on the compatibility among the translators and seamless integration of generated codes.
Keywords: Software Development Environment, Translator, Multi-paradigm.
1. INTRODUCTION
Improving the quality of software products and the productivity of software developers has been
an enormous challenge for the software industry. To respond to the challenge, many new design
and development methodologies and programming paradigms have been introduced. The
availability of modeling tools and rich sets of libraries and the adoption of design patterns and
application frameworks all contribute to produce better software systems today. Another rapid
evolving frontier in this campaign is the development of programming languages based on
different paradigms. In the context of computer science, a programming paradigm is defined as a
computational model [1] that a programming language is based on, i.e., the style or approach a
programming language uses to express problem solving plans. In the past forty years, several
generations of programming languages have been introduced based on the following four
dominant programming paradigms: imperative, functional, logic and object-oriented. Since real
world problems are much diversified, it is not surprising that some styles are better suitable to
solve some problems than others. Another observation is that for large sophisticated software, it
is likely that a single paradigm may not be enough to develop all parts of the system. This
naturally led to the pursuit of software development using programming languages with different
paradigms, i.e., multi-paradigm programming. The overall objective of multi-paradigm
programming is to allow developers to choose a paradigm best suited for the part of the problem
to be solved. As for how multiple paradigms can be deployed to build a single application, many
different routes have been taken to try to answer this question.
The translator-based multi-paradigm programming was first proposed in [6]. This approach allows
multi-paradigm programming by translating the source code written in different paradigms into a
target language code before they are integrated. [7] has demonstrated the feasibility of this
approach by developing a compiler for a functional programming language. However, there are
still some questions remain to be answered. How feasible and realistic is it to use this approach in

large scale real world application development? What are the main obstacles of deploying this
approach in real world?
The rest of this paper is organized as following. In the second section, the background of the
translator-based multi-paradigm is discussed. In the third section, we describe our experiment
with the translator-based multi-paradigm programming by implementing a centralized software
development platform SourceMerge, which allows for program development with logic, functional
and object-oriented programming languages. Using this platform, a calulator application is
developed with expression validation, evaluation and GUI components written in Prolog, Lisp and
Java respectively. Issues encountered during this experiment are also discussed in this section.
The final section summarizes our current work.
2. TRANSLATOR-BASED MULTI-PARADIGM PROGRAMMING
A programming paradigm is often defined as a computational model ([1]) that a programming
language is based on. In general, a programming language implements only a single paradigm.
For example, the imperative paradigm, with C as an example language, is identified by the use of
variables, assignment statements and explicit flow of control. The functional paradigm, with Lisp
as a representative, distinguishes itself in function definitions, recursion and the ability to create
high-order functions. Logic paradigm depends on rules and logic, and a main language
supporting this paradigm is Prolog. The object-oriented paradigm, featured by Java, uses class
inheritance hierarchy and polymorphism to create applications with dynamically reusable code.
Some modern programming languages can support more than one paradigm. For example, C++
supports both imperative and object-oriented paradigm and SICStus Prolog supports both logic
and object-oriented paradigm. Each paradigm has its strength and weakness in representing the
concepts and carrying out the actions of a specific application. Multi-paradigm programming is to
explore different ways to integrate the best features of each paradigm in software development.
Generally speaking, multi-paradigm programming can be accomplished either inside the same
programming language (i.e., language extension using multi-paradigm languages) or in a system
that assures a certain way of integration and interaction among separate processes or modules.
[2] and [3] proposes to use a multi-paradigm language. Rather than deciding what the correct
paradigm is to use, using a language that implements every paradigm can easily solve the issue
theoretically ([2]). The problem with this approach is that a language with many paradigms
intertwined would be too difficult for most programmers to learn and would be rather hard to
understand and debug applications written in such language. An emerging theme is the ability to
access one programming language from another ([4]). A good practice would suggest keeping
paradigms separated to allow for understandable code. [6] and [7] approach the problem by
translating a single language program into a target language such as C. While the approach is
credible, it restricts the abilities of multi-paradigm programming to only allowing source and target
paradigms to be used together. As one can see, all those approaches are limited in either the
number of paradigms can be combined and the degree of integration can be achieved.
Translator-based programming has been discussed in [1], [6], and [9]. The main idea is that
different parts of an application can be written in different programming languages; later those
different parts are translated into one target language; finally the translated source code in the
target language are compiled into a final executable by the target language compiler. A similar
approach surfaced after [6] allows for two languages to be written together in the same source
file(s) and to be translated/interpreted during compile time ([4]). This approach is much like
translator-based multi-paradigm programming except the code are written as if part of the same
language instead of being written in separate files as separate programs. [1] argues that after
comparing with all others, the translator-based multi-paradigm approach appears to be the most
viable and expandable solution since theoretically it allow any number of paradigms to be
integrated in a natural way and it is a much better compromise between ease of use and degree
of integration.

3. JAVA-CENTERED TRANSLATOR-BASED MULTI-PARADIGM PLATFORM
To answer the questions such as how feasible and realistic is it to use translator-based multi-
paradigm approach in large scale real world application development and discover the main
obstacles of deploying this approach, we developed a Java-centered translator-based multi-
paradigm platform SourceMerge. SourceMerge provides a simple interface for selecting source
files written in different paradigms and translated them into the target paradigm. In this case, Java
is selected as the target language and programs written in Lisp and Prolog representing logic and
functional paradigm are prime candidates to be translated. Once the selected source files written
in Prolog and/or Lisp are translated by their corresponding compilers respectively, SourceMerge
can collect them into a single location and generate all required libraries and packages and use
Java compiler to generate a single, standalone Java application.
3.1 Design Considerations
Java is selected as the target language in SourceMerge. Java’s object-oriented paradigm is much
more suitable for large-scale applications due to its capability for abstraction, inheritance and
polymorphism, easy-to-use language interface and its portability to any system that runs a Java
Virtual Machine. Java’s strength in describing real world objects and their behaviors with class
structure makes it natural to represent the concepts and actions to be carried in other paradigms
(such as functions in functional paradigm and predicate logic in logic paradigm). Java’s
sandboxing provides a security blanket that can protect a user from system crashes caused by
errors in translated code.
We choose logic and functional paradigms as the two candidate paradigms in SourceMerge.
However, as can be seen from Figure 1, the design of SourceMerge allows the inclusion of a
new paradigm to the system can be done easily (as demonstrated by the dashed line portion in
Figure 1) since the translation process for each paradigm is independent from the rest of the
system. SourceMerge acts as an adapter to translate multiple paradigms into a single target
paradigm. As long as a language translator follows the rules for generating output defined by
SourceMerge, it can be easily integrated into the system.
FIGURE 1: SourceMerge’s Select, Translate, Merge and Compile Process.
Figure 2 show the GUI of SourceMerge application. Three major tasks can be completed on this
interface: selection of source files, translation of the source code and merging of the final
executable. The execution status of translation and compilation is also displayed on the interface.
Source Code Selection
(Select all source files for the application)
Java Code Prolog Code Lisp Code
Prolog Cafe Linj
Merge Generated Java Code
Code in paradigm A
Translator A

FIGURE 2: SourceMerge Main Interface.
3.2 Translation Tools
Due to the time constraint for this study, we decided to use existing open source Lisp and Prolog
translators. After a thorough research over the Internet, we find that Prolog Cafe [9] and Linj [10]
are the only two freely available tools exist today that specifically meet the needs of translating
the Prolog and Lisp languages to Java.
The Prolog to Java translator Prolog Cafe is built on the de facto standard for Prolog compilers,
the Warren Abstract Machine (WAM) ([5], [11]). After translating Prolog sources to Java, the
execution model of the generated Java classes are also based on the WAM. Though this
produces difficult-to-read code and layers of terms to sort through, the translated output executes
cleanly and, in the Prolog aspect, quickly. Prolog Cafe is written in Java and therefore portable to
any platform with Java compiler and runtime environment. The generated source code requires
the inclusion of the Prolog Cafe Java libraries that implement the WAM algorithms. Additionally,
the compiled program still depends on a standalone interpreter within Prolog Cafe. This makes it
unsuitable to be embedded into other Java programs and we will address this development issue
further later.
Linj, the Lisp to Java translator, is open source and it translates from one source paradigm to
Java. To make the translation algorithm efficient and allow the programmer to follow the Lisp
programming conventions and still have the translated source follow all of Java’s rules, Linj
comes with its own language, respectively named Linj ([10]). The Linj language is syntactically
the same as Common Lisp except for packages, something that is ignored for this study, and the
existence of a null-term as opposed to an empty list. The Linj translator is written in Common Lisp
and the translated source code is purposed to be human-readable and efficient. There are no
specially required Java libraries to include so the individual classes generated can be compiled
as standalone programs, or embedded into other Java applications.
3.3 Encountered Issues
A major hindrance towards the research for this project is that: both of the translators, Prolog
Cafe and Linj, are no longer supported by their creator. Also, due to the limited user base of the
tools, community support and resources are scarce, if not nonexistent.
The first obstacle is that Prolog Cafe generates Java source code as a standalone application
running through a command-line interpreter that comes with Prolog Cafe. This execution model
does not fit into our design of the centralized environment that merges Java classes generated
select
source code
merge
code
add
source code
output

from different paradigms and compiles them into a single Java application. Since the command-
line interpreter for Prolog Cafe is also open source, and it also includes the same Java libraries
that are required to be included in the generated source code, this became the starting point of
tackling this issue. After stripping away the bells and whistles of the command-line interface of the
interpreter, it became visible that the same procedures are called to execute any translated code
each time. Therefore, for each Prolog source code, a specially defined template class, which gets
dynamically modified by SourceMerge, is used to produce the source suitable for integration with
other Java classes.
Along with no longer being supported, the documentation for Linj was never completed. There are
also no instructions as to how to install Linj nor the system requirements for installation. The Linj
translator uses direct Linux commands and the translation process must be performed under a
Linux system. This information is missing from the unfinished documentation. Another challenge
is that all required Lisp packages are not specified in the document either. So significant amount
of effort were made to determine the system requirements, write a parser to search through the
Linj translator to identify all packages used before the final Linj to Java translator running Linux
with the Steel Bank Common Lisp compiler was installed successfully.
Two similar issues affected both the Prolog Cafe and Linj translators from producing usable code
and neither were ever hinted at in documentation or other sources. The required Java libraries by
the source generated from Prolog Cafe don’t exist, until one translates them from Prolog to Java.
Since the interpreter provided with Prolog Cafe has a set of pre-compiled libraries required,
initially no errors were encountered when it was used alone. However, to include them into other
sources, they needed to be in their raw source and the errors started to show up. With Linj, the
translator successfully translates all basic Lisp programs to Java without an issue. However,
whenever non-basic expressions were used, such as a built-in function, compilation would silently
fail without any error messages. After significant time and effort spent on debugging, we found
that Linj requires a Lisp-package for each of the types being translated (such as mathematical
expressions, or vectors). Both of the issues were resolved eventually by letting SourceMerge
automatically supply the required Java libraries during translation.
3.4 Application Development Demonstration
To demonstrate the functionalities of SourceMerge, an arithmetic calculator program was created
under the SourceMerge environment. The Calculator application was written using all three
distinct paradigms allowed by SourceMerge: functional, logic, and object-oriented. Each paradigm
was used to write the part of the application that highlights the best features of this paradigm.
The Calculator can perform input validation and evaluate arithmetic expression. Java, the object-
oriented paradigm with rich GUI libraries, was used to create the Calculator’s GUI (see Figure 3-
4).

FIGURE 3: Expression Validation.
During the development of the Calculator, Prolog, the logic paradigm language, was used to
implement the validation function for the Calculator (Figure 3). Using predicate logic, the
validation of a proper arithmetic expression can be achieved by the following block of Prolog
code:
expr(L) :- num(L).
expr(L) :- append(L1, [+|L2], L), num(L1), expr(L2).
expr(L) :- append(L1, [-|L2], L), num(L1), expr(L2).
expr(L) :- append(L1, [*|L2], L), num(L1), expr(L2).
expr(L) :- append(L1, [/|L2], L), num(L1), expr(L2).
num([D]) :- number(D).
FIGURE 4: Expression Evaluation.
The expression evaluation of the Calculator was implemented using Lisp, the functional paradigm
language (Figure 4). Avoiding the easy-way of using Lisp’s eval, the source was designed to use
the prefix notation to operate on two numbers. The used method is as follows:
(defun expression(x/float operator/string y/float)
(cond ((string-equal operator "+") (+ x y))
((string-equal operator "-") (- x y))
((string-equal operator "*") (* x y))
((string-equal operator "/") (/ x y))
(t 0)))
As discussed earlier, during the implementation of the Calculator, each of the three involved
paradigms was used to implement a component that showcases the paradigm’s features most
suitable for the functionality of the component. The three kinds of source files were sent into
SourceMerge (see Figure 2) and the Prolog and Lisp files were successfully translated into Java
classes; these Java class files were all merged together; and a compiled Calculator application
was presented.
4. SUMMARY AND DISCUSSIONS
The Java-centered multi-paradigm software development environment SourceMerge built in this
study confirms that translator-based multi-paradigm software development approach is,
theoretically feasible for producing good quality software efficiently. SourceMerge demonstrates a
way to take source code from Prolog and/or Lisp, translates them into Java classes and has them
merge together to form a single application. This is an important and exciting step. What is even
important is to know what factors make this approach deployable in real world software
development. The experience in this study has shed some lights in answering these questions.

First of all, our experience shows that a centralized development similar to SourceMerge is
crucial to the success of translator-based multi-paradigm programming. It would be very difficult
and frustrating if a user has to go through many complex processes to accomplish the translation
and deal with the inconsistent behaviors and interfaces of the generated code. All the productivity
increase and quality improvement promised by the translator-based multi-paradigm programming
will be diminished by this difficulty.
Secondly, when building a centralized environment for multi-paradigm software development,
many important factors should be taken into considered. Multi-paradigm means not just one, two
or three paradigms to be used. It means that a centralized environment should be scalable
enough to accommodate as many paradigms as possible. To achieve this goal, the design of the
system should follow the Open-Closed design pattern, i.e., a new paradigm should be added to
the system easily and the update on the current paradigm translation process should not affect
other translation processes at all.
Thirdly, the selection of translators is the key to building a centralized multi-paradigm system. In
this study, two open source translators were selected. This decision was made due to our time
constraint. During our development process, we have encountered many unforeseen obstacles,
such as limited documentation, unknown system requirements and missing features. Another
obvious drawback with using existing translators is that the output code generated by the
translators of different paradigm may not be consistent. This will definitely make the integration of
the final executable very different if not impossible. We recommend that standards for the
translated code should be established and the design for each translator should base on the pre-
defined standards so that they can have consistent behaviors and interfaces. Although this
approach requires an upfront investment to build the translators, this will make the integration of
translated sources and the future extension of the system easier.
5. REFERENCES
1. R. Horspool and M. Levy. “Translator-Based Multiparadigm Programming”. Journal of
Systems and Software, 25, 39-49, 1993.
2. T. Budd and R. Pandey. “Never Mind the Paradigm, What About Multiparadigm Languages?”
SIGCSE Bulletin, 27, (2), 25-30, 1995.
3. D. Spinellis. “Programming Paradigms as Objective Classes: A Structuring Mechanism for
Multiparadigm Programming,” Ph.D. Thesis, University of London, 1994.
4. M. Carlsson et al. “SICStus Prolog User’s Manual”. Swedish Institute of Computer Science,
2011.
5. H. Ait-Kaci. “Warren’s Abstract Machine: A Tutorial Reconstruction”. MIT Press Cambridge,
1991.
6. P. Codognet and D. Diaz. “wamcc: Compiling Prolog to C”. In 12th
International Conference
on Logic Programming, MIT Press, 317 – 331, 1995.
7. M. Levy and R. Horspool. “Translating Prolog to C: a WAM-based approach”. In Proceedings
of the Second Computing Network Area Meeting on Programming Languages, and the
Workshop on Logic Languages, 1993.
8. X. Wang, “Compiling Functional Programming Languages Using Class Hierarchies”. M.Sc.
Thesis, Department. of Computer Science, University of Victoria, 1992.

9. M Banbara, N. Tamura, and K. Inoue. “Prolog Cafe: A Prolog to Java Translator System”.
INAP, 45-54, 2005.
10. A. Leitão. “Migration of Common Lisp Programs to the Java Platform -The Linj Approach
Linj”. 11
th
European Conference on Software Maintenance and Reengineering, 243 – 251,
2007.
11. D. Warren. “An abstract Prolog Instruction Set”. Technical Note 309, SRI International,
Menlo Park, CA, 1983.

Java-centered Translator-based Multi-paradigm Software Development Environment

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