Package: bison-doc
Version: 1:2.3.dfsg-4
Severity: wishlist
Hello Chuan-kai,
The documentation of YYLLOC_DEFAULT states that:
When defining `YYLLOC_DEFAULT', you should consider that:
* For consistency with semantic actions, valid indexes within the
right hand side range from 1 to N. When N is zero, only 0 is a
valid index, and it refers to the symbol just before the reduction.
During error processing N is always positive.
But it does not state what happens if N=0 for the first symbol,
and how YYLLOC_DEFAULT can deal with that.
For example if the grammar is
seq : /* empty */
| 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.
However the second reduction using this rule will have a symbol just before
the reduction.
Cheers,
Bill.
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