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From: gah4 <gah4@u.washington.edu>
Newsgroups: comp.compilers
Subject: Re: What stage should entities be resolved?
Date: Thu, 17 Mar 2022 17:06:15 -0700 (PDT)
Organization: Compilers Central
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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.)