PL/0 Compiler, written in Ruby

This is a simple one-step compiler, which generates valid Java Bytecode, written in Ruby.

More details can be found in the relatorio-compilador.pdf (pt-BR) document, but here is a summary:

• RSpec Specifications (Example Groups in test folder) are a good place to learn how the compiler should work.
• Sample PL/0 programs can be found in the test/fixtures directory.
• Automata (Finite State Machines) I'm using to parse code can be found in the lib/machine directory. They follow a domain specific language I've created in this project (lib/state_machine.rb) to describe automata.
• I am not using any parser generator, just because I wanted to deep learn how compilers work.
• The compiler generates Java Mnemonics, which are converted to Java Bytecode by the Jasmin assembler.
• The PL/0 grammar I'm following can be seen in the grammar.wirth file. It is written in the Wirth Syntax Notation.

Compiler Usage

The compile.rb file acts as the compilation entry point; it starts the hole process. The lib/ folder has the source code for all classes and the test/ folder has unit tests, using RSpec.

Minimum Requirements

• Java Runtime Environment (JRE) >= 1.5; the java command must be available in the $PATH environment variable.

Recommended Requirements

• Java Development Kit (JDK) >= 1.5;
• Ruby interpreter >= 1.8.5;
• java, ruby and rake commands must be in the $PATH;
• RubyGems - gem command available in $PATH.

Running with the minimum requirements

JRuby, the Ruby interpreter written n Java, is embedded in the compiler for machines with only the Java Runtime Environment installed. In this case, Ruby code is executed by JVM.

• inside of the compiler folder, create a new PL/0 file. There are some examples available in the test/fixtures folder;

• to see the compiler usage instructions, run the compile.bat file inside some shell (cmd inside Windows, or sh inside unixes);

• still in the terminal window, to compile your PL/0 source:

    compile <source> <output>
    compile program.pl0 compiled
  

• in this case, the compiler generates two files: compiled.j (Jasmin Mnemonics) and compiled.class (executable Java bytecode, assembled by Jasmin);

• to run the generated class, invoke the Java Virtual Machine:

    java compiled
  

Running with Ruby interpreter installed

• to run the compiler, use the compile.rb script:

    ruby compile.rb <source> <output>
  

• if you want to run the rspec tests in the test/ folder, just run rake test;

• spare some time reading the tests :-)

Troubleshooting

If you have some problem running the compiler, here is the full command line to be used:

java -cp jruby.jar org.jruby.Main compile.rb <source> <output>