On 8 May 2019, at 22:30, EML <address@hidden> wrote:
Sometimes, to make the grammar manageable, the lexer has to *dynamically*
return 'typename' instead of 'identifier'. Only semantic analysis can determine
what is a user-defined type (say 'foo'), so the lexer must be told at runtime
that 'foo' is a 'typename' and not an 'identifier'.
That is done by the method I indicated. In flex have a rule:
identifier [[:alpha:]][[:alnum:]]+
%%
{identifier} {
std::optional<std::pair<token_type, semantic_type>> x =
lookup_table.find(yylval.text);
if (!x)
return my::yyparser::token::identifier;
// Set semantic value return to x->second.
return x->first;
}
The Bison parser will then get the token of whatever the identifier has been
defined to. It will have rules like:
%token int_definition
%token int_variable
%token identifier
%%
definition:
int_definition identifier[x] value[v] {
lookup_table.push($x, {my::yyparser::token::int_variable, $v});
}
use_value:
… int_variable[x] … { … $x … }