Error reporting

[Nicolas Capens]

Hi,

Is there a mechanism to report more accurate lexical or syntax errors? For example, when the parser expects a constant but it finds something else, I would like to throw an exception with as description "Syntax error: expected constant, found 'x'".

I tried doing this by defining a keyword ANY like this:
<ANY: (~['x'] | ['x'])*>
and then in the parser section something like this:
constant() {/*accept const*/} | <ANY> {throw "expected constant";}

This works only half. In places where I expect a constant, it returns another error, like "expected constant declaration".

Is there an explanation for this? Should I use a totally different method? My apologies if this is already covered in the documentation...

[Alec Panovici]

Yes (full details in Sec. 3.5.5). In less detail, you can do something like this: get rid of the YACCish "ANY" thing and use exceptions:

() nice_constant()
{
  (accept_constant())
  catch (ParseException &pex)
  { // catch the original exception and throw a
    // customized one
    throw ParseException(pex.where(),
         "Constant expected.");
  }
}

If you don't like ParseException (say you want to hae just an error code, and keep the strings elsewhere):

() nice_constant() throw (MyException)
{
  (accept_constant())
  catch (ParseException &pex)
  { // catch the original exception and throw a
    // customized one
    throw MyException(pex.where(), ERR_42);
  }
}

Alec.

[Nicolas Capens]

Great! Thanks a lot Alec.