Frans Englich wrote:
state 118
72 SequenceType: ItemType .
73 | ItemType . STAR
74 | ItemType . PLUS
75 | ItemType . QUESTION_MARK
PLUS shift, and go to state 134
STAR shift, and go to state 135
QUESTION_MARK shift, and go to state 136
PLUS [reduce using rule 72 (SequenceType)]
STAR [reduce using rule 72 (SequenceType)]
$default reduce using rule 72 (SequenceType)
bison tells you in the output file that, in state 118, seeing PLUS or
STAR in its lookahead window, he cannot choose between shift (to states
134 and 135 respectively) and reduce (using rule 72: "SequenceType:
ItemType"). It seems that your SequenceType can be followed by a STAR
or a PLUS in some other rules (rules 17 and 20 to be precise), so when
bison has recognized an ItemType, he doesn't know which parsing action
to do, shift or reduce. The brackets indicate that the reduction will
not occur in front of PLUS or STAR because shift has the priority in bison.
In general, what you should do:
1) first try to remove the conflict by rewriting your grammar. This can
be difficult, and dangerous if you end up recognizing a language
different from the one you intended to parse.
2) otherwise find in which cases this shift/reduce conflict can occur,
and see if the default shift is good enough; if this is the case,
%expect is your friend.
3) otherwise try 1) harder.
4) turn to a GLR parser using %glr-parser.
Looking at your grammar, one can have the derivations
MutliplicativeExpr
=> MultiplicativeExpr STAR UnionExpr (rule 20)
=> UnionExpr STAR UnionExpr (rule 19)
=> InstanceOfExpr STAR UnionExpr (rule 28)
=> TreatExpr INSTANCE OF SequenceType STAR UnionExpr (rule 30),
and then
=> TreatExpr INSTANCE OF ItemType STAR UnionExpr (rule 72)
or
=> TreatExpr INSTANCE OF ItemType STAR STAR UnionExpr (rule 73)
This language is not easily generated in an LALR(1) grammar. Can you
modify it, for instance by adding parenthesis around the SequenceType?
state 134
74 SequenceType: ItemType PLUS .
$default reduce using rule 74 (SequenceType)
There is no conflicting shift action there, only a reduce.
--
Sylvain
_______________________________________________
Help-bison@gnu.org http://lists.gnu.org/mailman/listinfo/help-bison
