I think the C preprocessor was designed after the GPM clone m6, its successor m4, and Ratfor, so I suspect the difficulty in doing things like this is intention

I think the C preprocessor was designed after the GPM clone m6, its successor m4, and Ratfor, so I suspect the difficulty in doing things like this is intentional. I guess I should ask McIlroy, who is responsible for pushing m4 to its absolute limits and was present when the C preprocessor was being designed: https://www.cs.dartmouth.edu/~doug/barem4.m4 https://www.cs.dartmouth.edu/~doug/barem4.m4 _ Pure macros as a programming language _ _ m4 is Turing complete even when stripped to the bare minimum _ of one builtin: `define'. This is not news; Christopher _ Strachey demonstrated it in his ancestral GPM, described in _ "A general- purpose macrogenerator", The Computer Journal 8 _ (1965) 225-241. _ _ This m4 program more fully illustrates universality by _ building familiar programming capabilities: unlimited _ precision integer arithmetic, boolean algebra, conditional _ execution, case-switching, and some higher-level operators _ from functional programming. In support of these normal _ facilities, however, the program exploits some unusual _ programming idioms: _ _ 1. Case-switching via macro names constructed on the fly. _ 2. Equality testing by redefining macros. _ 3. Representing data structures by nested parenthesized lists. _ 4. Using macros as associative memory. _ 5. Inserting nested parameter symbols on the fly. _ _ Idioms 2 and 5 are "reflective": the program writes code _ for itself. It's very easy to get into enormous amounts of trouble in m4, m6, or GPM. The C preprocessor is not without its problems, but it is rare that I have difficulty in understanding why a given gcc -E invocation produces the output it does.