passing argument in campl4 ?

passing argument in campl4 ?

[Pietro Abate]

Hi all,

I've this small example below that I'd like to modify to
pass information top-down, from aa to bb (this is definitely
possible using parser and streams).

I see bb as a function but as it is translated (below below) 
is not entirely clear to me how I can pass a value from 

aa: [[ "AA"; c = bb "val" -> "aa"^c ]];
to 
bb arg: [[ a = INT; "BB" -> a ]];

I don't think this is directly possible (using the pseudo 
syntax above), but I was wonder if you have a trick to 
achieve something similar...

p


---------------- -------------------
(*pp camlp4o -I . pa_extend.cmo q_MLast.cmo *)

open Pcaml

let aa      = Grammar.Entry.create gram "aa"
let bb      = Grammar.Entry.create gram "bb"

EXTEND
   aa: [[ "AA"; c = bb -> "aa"^c ]];
   bb: [[ a = INT; "BB" -> a ]];
END

------------------dump ------------------------
(*pp camlp4o -I . pa_extend.cmo q_MLast.cmo *)

open Pcaml

let aa = Grammar.Entry.create gram "aa"
let bb = Grammar.Entry.create gram "bb"

let _ =
  Grammar.extend
    [Grammar.Entry.obj (aa : 'aa Grammar.Entry.e), None,
     [None, None,
      [[Gramext.Stoken ("", "AA");
        Gramext.Snterm (Grammar.Entry.obj (bb : 'bb Grammar.Entry.e))],
       Gramext.action
         (fun (c : 'bb) _ (loc : Lexing.position * Lexing.position) ->
            ("aa" ^ c : 'aa))]];
     Grammar.Entry.obj (bb : 'bb Grammar.Entry.e), None,
     [None, None,
      [[Gramext.Stoken ("INT", ""); Gramext.Stoken ("", "BB")],
       Gramext.action
         (fun _ (a : string) (loc : Lexing.position * Lexing.position) ->
            (a : 'bb))]]]


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Re: [Caml-list] passing argument in campl4 ?

[Hendrik Tews]

Pietro Abate <Pietro.Abate@anu.edu.au> writes:

   aa: [[ "AA"; c = bb "val" -> "aa"^c ]];
   to 
   bb arg: [[ a = INT; "BB" -> a ]];
   
The camlp4 reference manual
(http://caml.inria.fr/pub/docs/manual-camlp4/manual005.html) says
the syntax of a rule is 

   { pattern = } symbol ; ... { pattern = } symbol { -> action }

so you can't pass an argument to bb.

I can think two possible solutions:

1. Extend the camlp4 syntax for grammar extentions with a new
   metasymbol "bb" that takes one argument, similar to the
   metasymbols LIST0 and LIST1

2. Use something like

  aa: [[ x = do_the_aa_rule -> ... ]]

with 

let do_the_aa_rule = Grammar.Entry.of_parser gram "do_the_aa_rule" 
                        (* a (Token.t Stream.t -> 'a) function,
                           where 'a is the type of x above *)

The ocaml parser distributed with camlp4 contains examples for
the latter technique, see for instance infixop0 or test_label_eq
in camlp4/etc/pa_o.ml. Further, these sources seem to indicate
that there is no nice solution to your problem: The levels "||"
to "**" of the entry expr could benefit from some more
abstraction.

Bye,

Hendrik