Re: bison for nlp

[Akim Demaille]

> Le 9 nov. 2018 à 09:58, Hans Åberg <address@hidden> a écrit :
> 
> 
>> On 9 Nov 2018, at 05:59, Akim Demaille <address@hidden> wrote:
>> 
>>> By the way, I’ll still get the error message as a string I guess, right?
>> 
>> Yes.  Some day we will work on improving error message generation,
>> there is much demand.
> 
> One thing I’d like to have is if there is an error with say a identifier, 
> also writing the out the name of it.

Yes, that’s a common desire.  However, I don’t think it’s really
what people need, because the way you print the semantic value
might differ from what you actually wrote.  For instance, if I have
a syntax error involving an integer literal written in binary,
say 0b101010, then I will be surprised to read that I have an error
involving 42.

So you would need to cary the exact string from the scanner to the
parser, and I think that’s too much to ask for.    Not to mention the
case of super-long tokens, say a large string, or an ugly regex,
cluttering the error message.

I believe that the right approach is rather the one we have in compilers
and in bison: caret errors.

$ cat /tmp/foo.y
%token FOO 0xff 0xff
%%
exp:;
$ LC_ALL=C bison /tmp/foo.y
/tmp/foo.y:1.17-20: error: syntax error, unexpected integer
 %token FOO 0xff 0xff
                 ^^^^

I would have been bothered by « unexpected 255 ».