Re: What stage should entities be resolved?

On Thursday, March 17, 2022 at 11:41:47 AM UTC-7, Roger L Costello wrote:


(snip)


> For instance, as I understand it a C preprocessor goes through a C program and replaces macros. With this:


> #define PI 3.14


> the preprocessor will convert this:


> area = PI * radius * radius;


> to this:


> area = 3.14 * radius * radius;


> But if PI is inside a quoted string:


> "Today is PI day"


(You missed by a few days.)


> then the preprocessor does not replace PI.


As well as I know it, the early preprocessor, used by K&R C, did
substitute in strings. The current standard version does not, but some
versions have the --traditional option which might allow it.


It is not unusual to use the C preprocessor with --traditional for
Fortran programs, and some compilers will automate this. Some of the
processing done by the current C standard version messes up Fortran
programs too much.


Note, though, that the C preprocessor is pretty good at ignoring
almost anything, including mismatched quotes, between


#if 0


and the matching


#endif


The text doesn't need to look much like C at all, and can even have
mismatched quotes. It does have to properly process nested #if though.


The PL/I preprocessor isn't quite as forgiving.


At least in the early compilers, like early C compilers, it was
implemented as a separate pass, with intermediate disk file. I suspect
you can't put quite as much garbage between


%IF 0 %THEN %DO


and


%END


and especially likely not unmatched quotes. (PL/I uses apostrophes
for character constants, in both the language itself and the preprocessor.)


Java, on the other hand, does not have a preprocessor. The compiler is
supposed to know enough not to compile statements between


if(0) {


and


}


but I suspect that they need to look a lot like Java statements.
(You can also use a static final variable in such an if statement,
which the compiler knows how to evaluate at compile time.)

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