Re: how to get left hand side symbol in action

[Derek Clegg]

On May 10, 2019, at 6:47 AM, Hans Åberg <address@hidden> wrote:
> 
> 
>> On 10 May 2019, at 07:24, Akim Demaille <address@hidden> wrote:
>> 
>> 1. there is a real and valid need for the feature, which I still need
>>  to be convinced of, especially because symbol names are technical
>>  details!
> 
> One can also write better error messages by using these internal yytname_ 
> table names:
> 
> If one checks on a lookup table whether the name has been already defined and 
> it is, then one can give information about that already present name. For 
> example:
>  “name” {
>      std::optional<std::pair<token_type, semantic_type> x0 = 
> my::symbol_table.find($x.text);
> 
>      if (x0) {
>        throw syntax_error(@x, "Name " + $x.text + " already defined in this 
> scope as "
>          + yytnamerr_(yytname_[x0->first - 255]));
>      }
>    …
>  }
> 
> Right now, all parts are internal and may change: the token translation 
> x0->first - 255, yytname_ lookup, and error message cleanup yytnamerr_.

I agree with this — this has been an annoyance for me for years.

Derek