Ebo Compiler
The Ebo compiler can be any compiler for which translation tables (an Ebo Map) exist.
This demo uses a modified lcc compiler developed by Christopher W. Fraser, David R. Hanson, and Jacob Navia (Please see the readme file that comes with the download). The lcc compiler is a Windows 95/98 C compiler. The lcc compiler has been modified to read an Ebo file, translate it into an compilable source file, and compile that source file. A linker and resource compiler is also included so that an application can be created and run.
Ebo Map
The files used to map the symbols in the Ebo file to the keywords of the Windows and C are contained in the C:\zbo\bin\EboMap. There are six files.
- cEbo.txt contains the mappings (two symbols) for standard C procedure and constant names.
- hdrEbo.txt contains the mappings (one symbol) for the standard C header filenames.
- keyEbo.txt contains the mappings (one symbol) for standard C keywords.
- lccEbo.txt contains the mappings (one symbol) for lcc compiler specific keywords.
- winEbo.txt contains the mappings (two symbols) for Windows API
- resEbo.txt contains words which are not converted to the symbol format.
Speed
Compilation speed is fast because the compiler does not have to read as many characters as in the uncompressed source file. But the compiler is not as fast as it could be because of two things:
- All of the translation tables have to be read from the EboMap translation files at the beginning of the program.
- The modified lcc compiler does not directly compile the Ebo file, but it reads the Ebo file, converts its symbols into keywords and writes the result to disk (in C:\zbo\bin\EboTemp).
It is this temporary file which is actually compiled. This overhead slows down the compilation time. In future versions, the lexer and preprocessor will be rewritten to directly compile an Ebo file. Note: I actually did try to rewrite the lexer and the preprocessor to directly compile the Ebo file, but rewriting the preprocessor in the time frame in which I had was not possible (Now I wish I had taken that compiler class).
Future Enhancements
Translating the file before compilations serves my purpose for demonstrating the system. Further modifications to the compiler can result in more reductions in the Ebo file size.
One example is the translation tables for the Windows API. I assigned two character codes to every procedure, constant, structure, and element within the structures. Keeping all symbols the same length made the translation algorithm really easy and fast. But due to scoping, I could have made all elements within structures one character. The compiler would then have to be modified to recognized an element being referenced. This is possible because I do something similar in expressor when I'm converting user defined structures into symbols. This technique uses scoping to define the minimum number of symbols possible.
Also certain characters used in standard C can be eliminated. These characters help make the program readable by humans but are not necessarily needed by a modified compiler.
One example would be the opening parenthesis for procedures. The modified compiler knows if a symbol represents a procedure because the symbol lies within a certain range. Once the compiler reads the symbol representing a procedure; it knows it has a procedure and can go on processing arguments. There are probably many other ways the compiler can be improved.
Another modification in the compiler would be security features in which the compiler would prompt the user if the source file contains any commands which may be bad for the client's machine such as write or read commands to disks or execution of system commands. This feature would be necessary when the compiler is converted into a browser plug-in.
Execution
Currently, execution of an Ebo program is a manual process. The Ebo source file and a corresponding .bat file are downloaded from the web and placed in the bin folder. The user must double-click on the .bat file and execute it.
The .bat file does three things:
1. Launch lcc to compile the source file with the optimize flag turned on.
2. Link the object files
3. Launch the resulting executable.
In the future, I envision making the compiler a Browser plug-in. The plug-in would automatically download the Ebo file, recognize the language it represents, compile it with the appropriate compiler, and run the program in an appropriate window.