[ragel-users] EOF and token termination

[Brian Maher]

On Mon, Jun 28, 2010 at 10:21 AM, Adrian Thurston wrote:
> Just to be certain, you'd like a token at the end of the input to match even
> if it is not in a final state?

Yes.  Or to put it another way: I want to make eof be a valid final
state kind of like what the $ in perl compatible regular expressions
mean.

> If that's the case, I'm sorry I don't have an elegant solution for you. A
> state is either final or not, and what you need is to make all states final
> when at the end of the input.

Is there a way to say "make this state final when at the end of the
input"?  `fgoto final;` was my attempt at doing this, but it didn't
work ;-).

Thanks for your help!

Cheers,
-Brian

> On 10-06-27 06:46 AM, Brian Maher wrote:
>>
>> Hello Ragel Users,
>>
>> First, I just want to say that Ragel is an awesome tool, thank you
>> Adrian for sharing this tool with the open source community!
>>
>> Recently I've been trying to write a grammar for which individual
>> tokens may be pre-maturely terminated by EOF.  I came up with the
>> following rather hacky solution below (emit the same action as though
>> the token was "recognized", then fbreak so that only one token is
>> guaranteed to be "seen").  The things that I don't like with this
>> solution are that:
>>
>>   * I'm not keen on having to redundantly call the token's action in
>> two places since a maintainer later on may forget to update one of the
>> places where $eof(token_action) is done.
>>
>>   * te is not updated (although this isn't a big deal since I can just
>> use p instead of relying on te, and if I really wanted to make a fuss
>> about this I could always add $eof{te=p;}).
>>
>> One idea I had was to $eof{fgoto final;}, but that doesn't work since
>> the "final" label is only defined within the context of state charts
>> and can't be used as a "normal label".
>>
>> --------------example.rl
>>
>> #include<stdio.h>
>>
>> %% machine t;
>> %% write data;
>>
>> #define INPUT "abcd"
>>
>> int main() {
>>    char *ts, *te;
>>    int   cs, act, i;
>>    char *input = INPUT;
>>    char *p     = input;
>>    char *pe    = input + (sizeof(INPUT) - 1);
>>    char *eof   = pe;
>>
>>    fprintf(stderr, "Input[");
>>    fwrite(p, 1, pe-p, stderr);
>>    fprintf(stderr, "]\n");
>>
>>    %%{
>>        write init;
>>
>>        action text {
>>            fprintf(stderr, "Text [%c]\n", *p);
>>        }
>>
>>        action token {
>>            fprintf(stderr, "Token[");
>>            fwrite(ts, 1, p-ts, stderr);
>>            fprintf(stderr, "]\n");
>>        }
>>
>>        Token = "abc" "def" $eof(token) $eof{fbreak;};
>>
>>         main := |*
>>            Token =>  token;
>>            any   =>  text;
>>        *|;
>>        write exec;
>>
>>    }%%
>>    fprintf(stderr, "end\n");
>>    return 0;
>> }
>>
>> --------------/example.rl
>>
>> Thanks!
>> -Brian
>>
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>>
>
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--
Brian Maher >> Glory to God <<



-- 
Brian Maher >> Glory to God <<

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