Hans Aberg writes: > I thought "OR" was a terminal, and "expr" a nonterminal that may expand to > contain "OR" by the rule you listed as > expr -> expr OR expr
Yes, that's correct. But that's not the full story. I've posted it before,
but here it is again:
answer_statement: ANSWER expr answer_btn_list
...
;
answer_btn_list: WITH answer_btn_list_oneplus
| /* empty */
;
answer_btn_list_oneplus: answer_btn_list_oneplus OR expr
| expr %prec PSEUDO_MAX
;
expr contains a lot of things, expr OR expr is one of them.
> Which is causing the shift/reduce conflicts. Your answer gives me the
> impression that you may not understand how a grammar works.
Correct me if I'm wrong, but given:
answer "Hello" with "Cancel" or "OK"
the shift-reduce conflict is on the token "OR" after "Cancel". Bison could,
due to the ambiguous grammar, either shift OR (leading to reduction by expr
OR expr -> expr) or reduce (expr -> answer_btn_list_oneplus).
By default, it decided on shift. I didn't like that, so I now have that
%prec in there, which tells bison to reduce.
> The question is really: How do you want the rules
> expr -> expr OR expr
> x -> ANSWER expr WITH expr OR expr
> to be applied when the expression
> ANSWER expr WITH expr OR expr OR expr OR expr
> appears on top of the stack?
I hope the above answers that.
> But you have not told us whether
> answer "Hello" OR "world" with "Cancel" or "OK" or "Bye"
> is legal.
Well, syntacticly (is that a word?) it's legal. It would display a dialogue
with three buttons, except for the runtime error from "hello" and "world"
not being boolean values.
> So then you must have yet another rule you have not told us, either
> x -> ANSWER expr WITH "(" expr ")"
> x -> ANSWER expr WITH expr
Actually, it's one of the many things in expr: '(' expr ')'.
> I can only give my hunch of what the grammar might be (leaving it to Akim
> finding an efficient one):
I've tried changing the expr above to expr_orless and then adding a seperate
expr: expr_orless | expr OR expr, but that led to reduce-reduce conflicts. I
honestly didn't spend much time thinking about why.
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