Why isn’t (almost) pure C used instead of the C preprocessor?
Sure I understand it would be a little more verbose. For example:
#define PI 3.14159
If we had regular C as preprocessor language, the above could be rewritten to something like:
#define PI {printf("3.14159");}
The idea is to not substitute {printf(...)} for PI but to run the code from the macro definition and splice the output of that code in the place of PI.
Yes, it’s more verbose, but for more complex stuff I think it would help alot. Also, going with this design, programmers wouldn’t have to learn another language (namely the C preprocessor) in order to write macros.
So, are there any other reason except the verbosity that the C preprocessor is not just pure C (with perhaps small modifications, like the addition of the define keyword)?
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What you suggest is possible with more modern languages. C was invented at a time when compiler technology was far too primitive to allow this kind of programmable compilation pipeline. Furthermore, most programmers knew of no use for such a mechanism.
Even today it’s difficult to construct a compiler that can permit such programming. It’s easy to specify the behaviour in such simple cases but far more difficult to consider what it should do in the general case.
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