On these pages you can browse the source code for the BitC research compiler and examine its source documentation, which is still a work in progress. A few notes to help guide you into confusion as efficiently as possible:
There are two parsers at present. The S-expression parser is in SexprParser.y, and matches the specification. If it doesn't, it is a bug, and please tell us! The parser found in BlockParser.y is an incomplete experiment toward a provisional block-structured syntax. That parser remains incomplete; work on it has been temporarily set aside until objects and effect types are done.
The resolver and type checker are run after many passes, both as a sanity check and as a way to re-build information. The first pass through the type checker re-writes certain at_apply ASTs after types are established in order to simplify later processing.
Yes, sadly, the type checker really is that complicated, and it is about to become more so as we add support for effect types. The good news, such as it is, is that we are then going to declare ourselves done with it and move on. New AST nodes will get added to extend type checking into the property language, but that will hopefully (famous last words) be it.
1.4.7