This is another place where it's context-sensitive. To make everyone happy, I could rephrase my claim to "C preprocessor grammar is context-sensitive". This has

This is another place where it's context-sensitive. To make everyone happy, I could rephrase my claim to "C preprocessor grammar is context-sensitive". This has practical implications for e.g. what gets substituted where by the preprocessor. And in my claim this context-sensitivity means that we get different sequences of tokens in different places for the same input. Your example shows that we get different ASTs for the same input but different type information, although we still get the same sequence of tokens. Getting a different sequence of tokens is much more confusing to me than getting a different AST (or maybe I just got used to that with a life of experience with C++). But generally I disagree that preprocessor is separate from C for the following reasons: 1. It is specified by the C standard. 2. Different C compilers implement it differently, just like they implement other parts of C differently. 3. There is some truth in the claim that it is a separate text transformation, but here I also do not agree entirely, because the C standard doesn't say that the preprocessor outputs text. It says that it outputs tokens and those tokens are then converted to tokens of C proper[1]. It is also clear that this model of "text transformation" is also not entirely what happens in real world compilers, because if it did we wouldn't get good backtraces for tokens that went out of the preprocessor after substitution. Maybe GCC serializes it to text at some point, but clearly it gets more information out of it than what a naive interpretation of the phrase "text transformation" would suggest. [1]: Translation phase 7 of the C11 standard: > Each preprocessing token is converted into a token.