Re: Why token are numbered from 258?

[Akim Demaille]

> Le 7 févr. 2019 à 18:33, Peng Yu <address@hidden> a écrit :
> 
> Hi,
> 
> I don't quite understand why tokens are numbered starting from 258.
> What are 256 and 257 for? Thanks.
> 
> #define IF 258

256 is the error token, and 257 is the undef token (when we receive unknown 
tokens from yylex).

256 is mandated by POSIX :

https://pubs.opengroup.org/onlinepubs/007904875/utilities/yacc.html

> The token error shall be reserved for error handling. The name error can be 
> used in grammar rules. It indicates places where the parser can recover from 
> a syntax error. The default value of error shall be 256. Its value can be 
> changed using a %token declaration. The lexical analyzer should not return 
> the value of error.

It seems to say that we should be able to change the value with `%token error 
2400`, but we don't support that.  (checking...)  OMG, we do support it!  New 
test case...