Identifier Parsing - Redux

2018.09.20 · c++, boost, spirit x3

The ink hadn’t dried¹ on my Identifier Parsing post when I realized that there was indeed a better way to handle multiple keywords.

In that post I stated that a symbols<T> parser would not help because it suffered the same problem as lit(). Which is true.

What I missed was that, of course, you could use the same trick with symbols as you did with lit() to make it work.

Like this:

symbols<int>symtab;
symtabs.add("var")("func");

auto const reserved = lexeme[symtab >> !alnum];
auto const ident = lexeme[ +alnum - reserved ];

That does what we need.

And, we can fix up our lambda to automatically register new keywords.

auto mkkw = [](std::string kw) {
    symtab.add(kw);
    return lexeme[x3::lit(kw) >> !alnum];
};

Now, we can happily make up keywords and keep the rest of the parser in sync.

I will place a V4 in the Github repository.