Hello GNU Bison people,
I am using location tracking. While it works great in
general, there
is a corner case where I am unsure about the intended
behaviour of
bison and how the program should handle it.
The issue is what is the value of  $ for the first reduction
when the rule
involved has no components.
For example if the grammar is
%%
seq: /* empty */ {printf("empty: (%d, %d)n",$.first_line,$.first_column);}
| seq item
;
item: '(' seq ')'
;
%%
and the text to parse is "()", then the first
reduction will involve the
rule {seq : /* empty */} for which N=0, but there is no
symbol prior to
the reduction.
What is the output of this program according to the
specification ?
Is it different for a custom YYLTYPE and/or a custom
YYLLOC_DEFAULT ?
Looking at the parser code I see:
#if YYLTYPE_IS_TRIVIAL
/* Initialize the default location before parsing starts.
*/
yylloc.first_line = yylloc.last_line = 1;
yylloc.first_column = yylloc.last_column = 0;
#endif
which imply that the default YYLTYPE is handled specially.
Cheers,
Bill. (Please CC me)
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