[antlr-interest] Catching errors
Victor Giordano
power_giordo at yahoo.com.ar
Thu Feb 3 20:11:51 PST 2011
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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