Re: Parsing user-defined types

Hi Hans - thanks - that looks good.

On 08/05/2019 22:10, Hans Åberg wrote:
> 
>> On 8 May 2019, at 22:30, EML <[email protected]> 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 … }
> 
> 
> 


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