C++, libstdc++-v3 and, well, error messages

[Robert Dewar]

<<With the macro rewrite, in cpplib I implemented a feature where the
client can mark a spot in the token stream, and continue to get
tokens.  Some time in the future the client drops the mark; with the
option of returning to the marked spot (in which case getting tokens
repeats the delineated tokens), or to continue without returning.  The
client can even nest these marks, as long as they're popped LIFO
style.

If this were used in the existing C++ parser, it would probably make
it a lot cleaner.  I don't know whether the new recursive decent
parser will care, but I imagine it could be useful.
>>

A look ahead mechanism and backup mechanism like this can be very useful
indeed.