Projet Génie Logiciel: a compiler for Deca, a subset of Java
All Ensimag engineers have at least one project in common: the “Software
Engineering Project”, in French Projet Génie Logiciel, which consists of
three dedicated weeks of work in teams of five students. Goal: build a
full-blown compiler for a small object-oriented language. The target language
is jokingly called Deca, and looks like a subset of Java. Our compiler,
decac, must be written in Ada, and should output assembly code targeted at a
small virtual machine, built on purpose for this project.
Every good project should have an ASCII art banner. (Unfortunately that’s all I can put here, school policy forbids giving away project sources).
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During this project, I learned how to write Flex rules, how to build a syntax tree with Yacc and to decorate it. For this specific part, I had to implement and to test the rules of float propagation in numerical computations. I also wrote the data structure that took track of scope contexts during the parsing of class and method declarations.
I also learned how to generate assembly code that implemented dynamic linking of methods and used at most an arbitrary number of registers. Even if I did not code this part, I helped debugging it.
But the most interesting part for me was the implementation of the included
math functions, proposed in a way similar to Java’s Math utility class. We
had to provide sine, cosine, tangent and square root. This part was both
interesting and challenging, because we decided to write the math class in Deca
itself. It meant we had to compile our compiler without support for the math
class in a first time, then compile our math class to bytecode using our
compiler, and then recompile our compiler including support for our math class.
In the end, our compiler was considered by the professors to be of very good quality (except for a few bugs in lexical analysis - bad handling of case sensibility) and especially, our math class was pointed out as one of the most precise implementations.