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camlp4: precedence, LEFTA, NONA, etc.
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Date: -- (:)
From: Mauricio Fernandez <mfp@a...>
Subject: Re: [Caml-list] camlp4: precedence, LEFTA, NONA, etc.
On Thu, Mar 12, 2009 at 09:38:28AM +0000, Joel Reymont wrote:
>> To my understanding, precendence levels correspond to the level you
>> define in the grammar, in the given order : in your case, you have
>> "=", "+" at the same level, with higher precendence than "And" and
>> "*".
> What about this quote from the camlp4 manual?
>
> "An entry is composed of entry precedence levels, the first one being  
> the least precedent and the last one the most."
>
> I'm assuming that my expr counts as one rule where '+' and '=' have  
> lesser precedence than 'and' and '*' since those follow after.

In case of doubt, it's better to refer to Camlp4RevisedParser.ml, as said
before (I don't even remember where the camlp4 manual is, I just open that
file routinely when I'm about to do some camlp4 hacking :). In
Camlp4RevisedParser.ml, expr is defined as:

    expr:
      [ "top" RIGHTA
      ...
      | "+" LEFTA
        [ e1 = SELF; op = infixop2; e2 = SELF -> <:expr< $op$ $e1$ $e2$ >> ]
      | "*" LEFTA
      ...
        | e1 = SELF; op = infixop3; e2 = SELF -> <:expr< $op$ $e1$ $e2$ >> ]
      (infixop3 is *, / or %)
      | "**" RIGHTA
      ...
      | "unary minus" NONA
        [ "-"; e = SELF -> mkumin _loc "-" e
        | "-."; e = SELF -> mkumin _loc "-." e ]

So the levels are indeed listed in increasing order of precedence.

This might be of use, despite being for camlp4 pre-3.10:
http://martin.jambon.free.fr/extend-ocaml-syntax.html#priorities

-- 
Mauricio Fernandez  -   http://eigenclass.org