Preprocessor backing up

[Norman Diamond]

In article <11163 at smoke.BRL.MIL> gwyn at brl.arpa (Doug Gwyn) writes:

>... as a general design principle the preprocessor is not required to
>back up, apart from the quite limited case of rescanning the
>replacement buffer.

Thank you for answering my question, but I think that your answer might
be a bit too broad.  Section 3.8.3.4 (Dec. 7 '88) says that after
replacement, the replacement buffer must be rescanned WITH THE REST OF
THE SOURCE FILE'S PREPROCESSING TOKENS.

For example, consider:

  #include <stdio.h>
  #define mf1(x) printf("Hello, world.\n")
  #define m2     (z);
  main(){
    mf1 m2
  }

After "m2" changes into "(z);", it must be rescanned with the rest of
the source file's preprocessing tokens.  At this time mf1 must be
recognized as a function-like macro call.  The preprocessor MUST BACK
UP EARLIER THAN THE REPLACEMENT BUFFER.

I will bet that every pre-ANSI compiler/preprocessor would have
rejected the above program.  But ANSI requires it to print
"Hello, world.\n".

In fact I think I can construct a few perverse macros, which will make
the preprocessor take EXPONENTIAL TIME in proportion to the length of
the program.

-- 
Norman Diamond, Sony Corp. (diamond%ws.sony.junet at uunet.uu.net seems to work)
  The above opinions are inherited by your machine's init process (pid 1),
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