Hi Luke,
Syntax example:
printf<_S("John %d, %s %d\n")>(11, "Joe", 13);
Yay! That syntax doesn't suck. The _S would be BOOST_S if it were a boost library, I guess, or perhaps BOOST_MPL_STRING if we want to be very descriptive. Too bad we need the macro. It would be nice to jet get a variadic template instantiation from the language if we wrote printf<"John %d, %s, %d\n"> directly. It is pretty obvious that we can take this idea and run with it to do something really evil like:
ruby<_S("_1.each {|item| puts item }")>(my_array);
or
perl<_S("foreach $item (@_1){ print "$item\n"; }")>(my_array);
Man is that evil. Right up there with overloading the comma operator evilness. Ok, now, hands please, who wants to implement a Ruby interpreter as a template metaprogram? If you look at https://github.com/sabel83/mpllibs/blob/master/mpllibs/metaparse/string.hpp I call this macro MPLLIBS_METAPARSE_STRING (given that the library is called that at the moment - we can change it to BOOST_* when it goes in). _S is just an "alias" of it to simplify its usage. The shorter the name, the less disturbing it is.
If not for Perl, but for small EDSLs it may worth writing a parser (with some TMP tricks these compile-time strings could be compiled into C++ functions - no example for it yet). Given the error reporting capabilities of the parsers built using the library (demonstrated in https://github.com/sabel83/mpllibs/tree/master/libs/metaparse/example/parsin...) it may be useful/helpful. Regards, Ábel