glr parser and getting semantic values from the lexer

I feel real dumb asking this but,

How do you pass values back from the lexer when using %glr-parser?

I know I must use POD data types.
In the .y file, I am using:

%define api.value.type union
%token <int64_t> CONSTANT

and in the lexer file:
{inum}	{	// Integer
		int64_t number = strtol(yytext, NULL, 10);
		??? = number; // What do I do here?
		return MyPrefix::MyParser::token::CONSTANT;
	}

yylval is not defined. I have read you shouldn't really modify it anyways,
for reasons mentioned in the manual (which make sense).

My only other project was parsing a small portion of SQL. I used variants
and everything worked quite well for that project, but I know I can not
use variants here.

I'm really stumped here. Can anybody advise?

Thanks.