Annd what do you think about new keywords added in C++ like "class, public, private, protected, throw, catch": older C programs would no longer compile if these were variables. And most compilers have introduced their own keywords (sometimes with the convention of using "__" prefixes that should be reserved for keywords of the language).
Why did not Lua enforce that the "__" prefix should be reserved to core language extensions ?
It would have been easier to extend new keywords like "__const". But unfortunately, Lua has no naming convention at all for the allowed identifiers used in programs.
Another way to extend the set of keywords for future versions of Lua (while keeping existing Lua programs valid) would be to use a prefix that is currently forbidden for identifiers and not used by existing operators in expressions where identifiers would be used: e.g. "#" or "\" or "?" or "!"
Note that Java chose to use "@" (not for new lexical elements but for adding annotations in a set which is extensible by programs)
So instead of "const", why not "#const" or "\const", or "@const", or "?const", or "!const", if Lua introduces annotations but with a convention on naming (such as reserving lowercase ASCII initials a-z for core annotations defined by the semantics of the language, but still allowing programmers use all the annotations they want by using capital initials after the [#\@!?] prefix, or even an "_" initial if they wish, or
or non-ASCII letters if the syntaxic parsers allows UTF-8 encoding for source files)
