[antlr-interest] [Bulk] Re: Catching errors

[Victor Giordano]

Thanks Michael! I will take a look.. as far as we know, there are many 
ways to handle grammars errors, but i have certainly doubts about this, 
beacause the catch statement inside the grammar (at the bottom of the 
parser rule) doesn't catch the errors that suggest or, most probably, 
i'm not understanding how it work's... but, again, as far i see, i am 
not the only one having problems with this matter.

I hope to put an end to that je!.
Well thanks again!.

El 05/02/2011 03:20 a.m., Michael Bedward escribió:
> Hello Victor,
>
> This question that I posted last week describes how I am raising an
> error on unwanted input before EOF which, I think, is similar to what
> you are trying to do...
>
> http://antlr.1301665.n2.nabble.com/best-practice-for-unwanted-input-before-EOF-td5964792.html
>
> I was looking for a better way (no one has replied so far) but it does work.
>
> Michael
>
> On 4 February 2011 15:11, Victor Giordano<power_giordo at yahoo.com.ar>  wrote:
>> Hello people, two days a posted this problem and i still having troubles
>> with this matter, pliz give a hand, if you can of course....
>> I need to handle the errors of parsing in order to display a nice user
>> message.
>>
>> I am watching when i use the generated lexer and parser (Generated from
>> the LinearMath grammar below) in a java application is that do really
>> emit somekind of warning about two thinks:
>>
>> 1)extraneous input '<some_token>' expecting EOF *Only when a append the
>> EOF token at the end of the rule*
>> 2)required (...)+ loop did not match anything at input<some_token>'
>> *Only when i use the '+' quantity token modifier*
>>
>> where<some_token>  there is actually token.
>>
>> The matter is, again, how do i catch in a exception those errors. I show
>> below the grammar with an input example to try for yourself:
>>
>> grammar LinearMath;
>>
>> tokens
>> {
>>        PLUS     = '+';
>>        MINUS     = '-';
>>        MUL        = '*';
>>        DIV        = '/';
>> }
>>
>> inecuation:    linexpr ((RELATIONSHIP) linexpr)+ EOF!;
>> catch [UnwantedTokenException ute]
>> {
>>      System.out.println ("inecuation UnwantedTokenException  " +
>> ute.toString());
>>      throw ute;
>> }
>>
>> linexpr : (MINUS|PLUS)? linterm ((PLUS|MINUS) linterm)* EOF;
>>
>> linterm : factor? ID;
>>
>> expr returns [double value]
>>        : e=term {$value = $e.value;}
>>        (    PLUS e=term {$value += $e.value;}
>>        |    MINUS e=term {$value -= $e.value;}
>>        )*;
>>
>> term returns [double value]
>>        : f=factor {$value = $f.value;}
>>        (    MUL f=factor {$value *= $f.value;}
>>        |    DIV f=factor {$value /= $f.value;}
>>        )*;
>>
>> factor returns [double value]
>>        : DOUBLE {$value = Double.parseDouble($DOUBLE.text);}
>>        | '(' e=expr ')'{$value = $e.value;};
>>
>> ID  :    ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*;
>>
>> DOUBLE
>>        :   ('0'..'9')+
>>        |    ('0'..'9')+ '.' ('0'..'9')* EXPONENT?
>>          |   '.' ('0'..'9')+ EXPONENT?
>>          |   ('0'..'9')+ EXPONENT
>>          ;
>>
>> fragment EXPONENT : ('e'|'E') ('+'|'-')? ('0'..'9')+ ;
>>
>> NEWLINE:'\r'? '\n' { $channel = HIDDEN; };
>>
>> WS  :   (' '|'\t'|'\n'|'\r')+ { $channel = HIDDEN; };
>>
>>
>> RELATIONSHIP :    '<'|'<='|'='|'>'|'>=';
>>
>> and with the following input: "x<    y x"
>> that isn't a valid inecuation beacause the y x must have a binary
>> aritmetic operator (PLUS OR MINUS). The parser do his job very well, he
>> consume the "x" then "<" later "y" and when it reachs the seconds "x" it
>> emits an "UnwantedTokenException". The think is, that i am not being
>> able to catch it, and display an error to the final user. Look that i am
>> using to parse that input the inecuation "rule".
>>
>> --------------------------------------------------------------------------
>> 2) Other thing is about invalid tokens, i manage to treat then
>> overriding a member function of the lexer called nextToken(), like this:
>>
>> @lexer::members
>> {
>>      @Override
>>      public Token nextToken()
>>      {
>>          while (true) {
>>              state.token = null;
>>              state.channel = Token.DEFAULT_CHANNEL;
>>              state.tokenStartCharIndex = input.index();
>>              state.tokenStartCharPositionInLine =
>> input.getCharPositionInLine();
>>              state.tokenStartLine = input.getLine();
>>              state.text = null;
>>              if ( input.LA(1)==CharStream.EOF ) {
>>                  return Token.EOF_TOKEN;
>>              }
>>              try {
>>                  mTokens();
>>                  if ( state.token==null ) {
>>                      emit();
>>                  }
>>                  else if ( state.token==Token.SKIP_TOKEN ) {
>>                      continue;
>>                  }
>>                  return state.token;
>>              }
>>              catch (RecognitionException re) {
>>                  reportError(re);
>>                  throw new RuntimeException("Invalid Character  : " +
>> (char) (re.c));
>> // or throw Error
>>              }
>>          }
>>      }
>> }
>> ¿It's that the correct way?
>>
>> Ok, so far this.
>> Sorry for the bombing III of emails!. Thanks for advance.
>> Víctor.
>>
>>
>> El 03/02/2011 12:36 a.m., Victor Giordano escribió:
>>> I am watching when i use the generated lexer and parser (Generated from
>>> the LinearMath grammar below) in a java application is that do really
>>> emit somekind of warning about two thinks:
>>>
>>> 1)extraneous input '<some_token>' expecting EOF *Only when a append the
>>> EOF token at the end of the rule*
>>> 2)required (...)+ loop did not match anything at input<some_token>'
>>> *Only when i use the '+' quantity token modifier*
>>>
>>> where<some_token>  there is actually token.
>>>
>>> In fact the warnings is actually are a strings sended to the standart
>>> error.
>>>
>>> The matter is, again, how do i do to manage those errors altering normal
>>> flow with a real exception and treating it like one.
>>> Ok, so far this.
>>> Sorry for the bombing of emails!. Thanks for advance.
>>> Víctor.
>>
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>