Re: [Caml-list] Problem with precedence declaration in .mly file

[Oliver Bandel <oliver@first.in-berlin.de>]

Zitat von Angela Zhu <angela.zhu@cs.rice.edu>:

> Hi all,
>
> I have some problem with precedence declaration in OCaml parser.
> If I what to say exponential(ATOB) is prior to *(STAR) and / (DIVIDE),
>   * and / are prior to +(PLUS)  and -(MINUS),
> I wrote the following in the parser:
>
>
> /***** Precedence Rules  *****/
> ...
> %left PLUS MINUS
> %left STAR DIVIDE
> %left ATOB
> ...
>
> But I still have the following problems:
> (1) It appears that the parser
> reads "test = 2^2 + 7;" as "test = 2^9" instead of "test = 4+7", which
> would follow the conventional order of operations.
>
> (2)It also interprets "test = (1^2)/3 + 1;" as "test = (1 ^ 2
> / (3 + 1));"
>
> Can any one help me to see why it happens? Why the precedence rules
> doesn't work?
[...]

Precedences also can be created by sophisticated
organization of the grammar rules.

So, if your grammar rules may have a contradictory
meaning, then your parser works not as expected.

In general I would use the precedence-declarations only,
when you run into parser conflicts, if you don't use them.
When developing a grammr, I would recommend, first to start
with the grammar rules, and add precedence-/associatitivity-
declarations, at the end, if really necessary.


What is the rest of your mly-file?

A complete example would be helpful.


Ciao,
   Oliver