Re: How to change default outcome of shift/reduce conflict?

[Anthony DeRobertis]

Hans Aberg writes: 

> There are different styles of handling this problem. One is trying to alter
> the shift to reduce somehow; I think that the Bison manual say something
> about that (in the section about IF ... THEN ... ELSE).

Lookin in the "Shift/Reduce" section of "Algorithm", I don't see anything to 
this effect. 

> The other, which I prefer myself, is to rewrite the grammar so that it is
> not ambiguous anymore:

The best I have managed to do, is to do something like this: 

expr_orless: (everything that was in expr, except or)
         ; 

expr: expr_orless
  | expr OR expr
  ; 

answer_btn_list_oneplus: answer_btn_list_oneplus OR expr_orless
                     | expr_orless
                     ; 

This, does get rid of that shift-reduce conflict. However, it gives me two 
reduce/reduce conflicts instead. Not quite sure why I'm getting those 
reduce-reduces conflicts (even with -v bison doesn't seem to want to say 
much) 

I'd really like if there was a way to tell bison to prefer reduce over shift 
in a given state. After reading the source, and watching bison work in a 
debugger, it appears %prec applied to the rule will do what I want. So I now 
have: 

answer_btn_list_oneplus: answer_btn_list_oneplus OR expr    { ... }
                       | expr   %prec PSEUDO_MAX            { ... }
		       ;

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