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Re: traditional cpp

>    #define FOO foo /*
>    #undef FOO
>    #define FOO bar */
>    FOO

> would yield

>    bar */

> which definitely isn't right either.

Depends on where you stand on preprocessor lines containing a
begin-comment sequence without a matching end-comment sequence.

In this case, you seem to think this thing begins a comment (on the
first line, ended on the third line).  But in your example

    #define STOP */
    #define START /*
    /* hello there STOP fnord START ho hum */

this would lead to considering the second line to begin a comment which
includes all of the third line.

> But if you drop comments on directive lines *before* expansion to
> make this problem go away, the /**/ comments used for token pasting
> disappear and nothing works.

There's a difference between comments on directive lines and comments
partially on directive lines.

> I'm now really curious what a genuine legacy cpp really does.

I played a hunch which was telling me I had a CD or two from PUPS
kicking around.  I managed to find it; among other things, it has what
appears to be real 4.3BSD on it, including a "new version" of cpp which
"was written by John F. Reiser".

It fireworks rather badly when I try to build it; I'll be trying to
coax it into building.  If I succeed I'll thrown these tests at it.

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