Boo uses the ANTLR parser generator to create the parser for boo source code.
The parsing rules are defined in the boo.g grammar file included with the boo source distribution.
Here is a diagram of the boo syntax, generated automatically from the boo.g file via the syndiag tool.
Right now boo uses ANTLR's C# code generater and runtime library to generate and run the boo parser. We also have a boo code generator for ANTLR which we will switch to in the future.