[ragel-users] EOF and token termination

Brian Maher brimworks at gmail.com
Sun Jun 27 13:46:45 UTC 2010

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".


#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;



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