You can get quite far with a preprocessor that's completely unaware of the semantics of the code. Or that trusts the programmer to use the macros on constructio

You can get quite far with a preprocessor that's completely unaware of the semantics of the code. Or that trusts the programmer to use the macros on constructions of the right type. Even parsing C "correctly" is a huge problem, since the syntax is ambiguous and the ambiguity can only be resolved by keeping a symbol table that tracks what kind of thing a symbol is. So there's a huge pragmatic force to keep a strict separation between a type-unaware preprocessor and a full-blown compiler frontend. (I considered using clang to dump the C AST when building cmacro, but concluded it would be too unwieldy.)