Here I am, after a few months of silence. Now I want to share my experience of making some sort of a compiler. The task is part of my studying at Master’s.

So, basically I should write a program in C. The program takes an input of one or more files that contain a code in my language (well, the syntax it should follow is given by a teacher) and produce an output - an executable file.

The first thing to do is to build an Abstract Syntax Tree (AST). For this purpose I use ANTLR3. It’s such a tool that allows you to write syntax rules for your language. I’ve written simple rules regarding: function signatures and calls, parameters, various expressions, types, and etc. All of it you can see here.

Using antlr-3.5.3-complete.jar on MyLanguage.g file I get lexer and parser sources and headers that are going to be utilized in my program sources.

Then antlr-runtime-c library was required for successful build. I’ve taken it by copy-pasting for the lack of time and experience of working with the third-party open-source libraries. Not sure whether it matters or not, I have no experience with software licenses as well.

So, to my code. I wrote a simple main() function that reads an input file and produces an AST structure. To present the result AST the Graphviz library is used. And thanks to antlr-runtime-c lib there is a function makeDot() that produces a file of DOT format that is readable by Graphviz library:

pANTLR3_STRING dotString = parser->adaptor->makeDot(parser->adaptor, tree);

fprintf(dotFile, "%s", (char*)dotString->chars);
fclose(dotFile);

There is a .dot file shows up after execution of the program. By the command dot -Tpng output.dot -o output.png it is being converted into .png format so that you can easily see the AST.

Also I made some modifications to the AST that is taken from ANTLR library functions, namely rotation of function calls and array accesses. ANTLRv3 (the 3rd version) does not allow left-recursive expressions, that’s why there is suffixes in syntax rules and not prefixes. This is requirement from teacher that function calls and array accesses should be left-recursive, and I did it.