try .. finally using new camlp4

try .. finally using new camlp4

[Jon Harrop]

I'm just getting my toe wet with the new camlp4 and I can't get this simple 
syntax extension to work. AFAICT, the following code:


open Camlp4.PreCast;;

let expr : Camlp4.PreCast.Ast.expr Camlp4.PreCast.Gram.Entry.t =
  Gram.Entry.mk "expression"

module Example (Syntax : Camlp4.Sig.Camlp4Syntax) = struct
  open Camlp4.PreCast
  include Syntax

  let printer =
    let module P = Camlp4.Printers.OCaml.Make(Syntax) in
    new P.printer ()

  EXTEND Gram
    expr: LEVEL "top"
    [[ "try"; f=expr; "finally"; g=expr ->
	 <:expr<
	   ((function
	     | `Val v, g -> g(); v
	     | `Exn e, g -> g(); raise e)
	      ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
	 >>]];
  END
end

module M = Camlp4.Register.OCamlSyntaxExtension(Id)(Example)


should provide the syntax extension. Compile with:

$ ocamlc -dtypes -pp camlp4of -I /usr/lib/ocaml/3.10.0/camlp4 -linkall 
camlp4lib.cma unix.cma Camlp4Parsers/Camlp4OCamlRevisedParser.cmo 
Camlp4Parsers/Camlp4OCamlParser.cmo Camlp4Printers/Camlp4AutoPrinter.cmo 
Camlp4Bin.cmo pa_tryfinally.ml -o pa_tryfinally

Drop into a top-level with the extended syntax and the extension works but it 
seems to have replaced the original try .. with syntax rather than added a 
new one:

$ ocaml camlp4of.cma pa_tryfinally.cmo
        Objective Caml version 3.10.0

        Camlp4 Parsing version 3.10.0

# try raise Exit finally print_endline "Foo!";;
Foo!
Exception: Pervasives.Exit.
# try raise Exit with _ -> print_endline "Foo!";;
Parse error: "finally" expected after [expr] (in [expr])

I've tried various things to correct this but I can't get it to work. What am 
I doing wrong?

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The OCaml Journal
http://www.ffconsultancy.com/products/ocaml_journal/?e

Re: [Caml-list] try .. finally using new camlp4

[Julien Moutinho]

> Drop into a top-level with the extended syntax and the extension works but it 
> seems to have replaced the original try .. with syntax rather than added a 
> new one:

Interestingly, here is what your code does
with the current CVS version <http://camlcvs.inria.fr/>:

$ ocaml camlp4of.cma pa_try_finally.cmo
        Objective Caml version 3.11+dev2 (2007-05-08)

        Camlp4 Parsing version 3.11+dev2 (2007-05-08)

# try raise Exit finally print_endline "Foo!";;
Foo!
Exception: Pervasives.Exit.
# try raise Exit with _ -> print_endline "Foo!";;
Foo!
- : unit = ()

Re: [Caml-list] try .. finally using new camlp4

[Vincent Hanquez]

On Sun, Jul 08, 2007 at 01:14:41AM +0100, Jon Harrop wrote:
> I'm just getting my toe wet with the new camlp4 and I can't get this simple 
> syntax extension to work. AFAICT, the following code:

A bit OT, but I found it quite easy to actually hack ocaml source
directly to do the right thing for try finally. My modification seems to
works correctly, without having any deep knowledge of ocaml internal
compiler code. 

>   EXTEND Gram
>     expr: LEVEL "top"
>     [[ "try"; f=expr; "finally"; g=expr ->
> 	 <:expr<
> 	   ((function
> 	     | `Val v, g -> g(); v
> 	     | `Exn e, g -> g(); raise e)
> 	      ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
> 	 >>]];
>   END

I don't know camlp4, but why don't you use a more straightforward
(let r = try f() with e -> g(); raise e in g(); r) construct
instead of wrapping/unwrapping the thing into polymorphic variant ?

Cheers,
-- 
Vincent Hanquez

Re: [Caml-list] try .. finally using new camlp4

[Vincent Hanquez]

On Mon, Jul 09, 2007 at 10:43:04AM +0100, Jeremy Yallop wrote:
> Jon's version avoids name capture.  If the user writes
> 
>    let r = 1 in
>      try
>        2
>      finally
>        print_endline (string_of_int r)
> 
> then your version (modulo the unit arguments) expands into
> 
>    let r = 1 in
>       let r = try 2
>               with e ->
>                  print_endline (string_of_int r);
>                  raise e in
>            print_endline (string_of_int r);
>            r
> 
> which prints "2" instead of "1".

indeed,
Thanks,
-- 
Vincent Hanquez

Re: [Caml-list] try .. finally using new camlp4

[Jeremy Yallop]

Vincent Hanquez wrote:
>>   EXTEND Gram
>>     expr: LEVEL "top"
>>     [[ "try"; f=expr; "finally"; g=expr ->
>> 	 <:expr<
>> 	   ((function
>> 	     | `Val v, g -> g(); v
>> 	     | `Exn e, g -> g(); raise e)
>> 	      ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
>> 	 >>]];
>>   END
> 
> I don't know camlp4, but why don't you use a more straightforward
> (let r = try f() with e -> g(); raise e in g(); r) construct
> instead of wrapping/unwrapping the thing into polymorphic variant ?

Jon's version avoids name capture.  If the user writes

    let r = 1 in
      try
        2
      finally
        print_endline (string_of_int r)

then your version (modulo the unit arguments) expands into

    let r = 1 in
       let r = try 2
               with e ->
                  print_endline (string_of_int r);
                  raise e in
            print_endline (string_of_int r);
            r

which prints "2" instead of "1".

Jeremy.

Re: [Caml-list] try .. finally using new camlp4

[Nicolas Pouillard]

On 7/8/07, Jon Harrop <jon@ffconsultancy.com> wrote:
>
> I'm just getting my toe wet with the new camlp4 and I can't get this simple
> syntax extension to work. AFAICT, the following code:
>

Let's go

>
> open Camlp4.PreCast;;
Useless since you use the functor based approach.

> let expr : Camlp4.PreCast.Ast.expr Camlp4.PreCast.Gram.Entry.t =
>   Gram.Entry.mk "expression"
Useless too why make a new (empty) rule, there is already one that one
wants to extend.

> module Example (Syntax : Camlp4.Sig.Camlp4Syntax) = struct
>   open Camlp4.PreCast
Useless too

>   include Syntax
>
>   let printer =
>     let module P = Camlp4.Printers.OCaml.Make(Syntax) in
>     new P.printer ()
Useless too

>   EXTEND Gram
>     expr: LEVEL "top"
>     [[ "try"; f=expr; "finally"; g=expr ->
Here one extend a rule. So in order to have something working properly
one *must* look at the original rule.

There is the up-to-date rule:

$ cvs ann -r release310
camlp4/Camlp4Parsers/Camlp4OCamlRevisedParser.ml | grep '"try"'
Annotations for camlp4/Camlp4Parsers/Camlp4OCamlRevisedParser.ml
***************
1.2.2.11     (pouillar 04-Apr-07):         | "try"; e = sequence;
"with"; a = match_case ->

So the correct rule is:
     [[ "try"; f=sequence; "finally"; g=expr ->

>          <:expr<
>            ((function
>              | `Val v, g -> g(); v
>              | `Exn e, g -> g(); raise e)
>               ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
>          >>]];
>   END
> end
>
> module M = Camlp4.Register.OCamlSyntaxExtension(Id)(Example)

The Id module is missing...

So there is the fixed code:

module Id = struct
  let name = "pa_tryfinally"
  let version = "$Id:$"
end

module Example (Syntax : Camlp4.Sig.Camlp4Syntax) = struct
 include Syntax

 EXTEND Gram
   expr: LEVEL "top"
   [[ "try"; f=sequence; "finally"; g=expr ->
        <:expr<
          ((function
            | `Val v, g -> g(); v
            | `Exn e, g -> g(); raise e)
             ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
        >>]];
 END
end

module M = Camlp4.Register.OCamlSyntaxExtension(Id)(Example)

>
> should provide the syntax extension. Compile with:
>
> $ ocamlc -dtypes -pp camlp4of -I /usr/lib/ocaml/3.10.0/camlp4 -linkall
> camlp4lib.cma unix.cma Camlp4Parsers/Camlp4OCamlRevisedParser.cmo
> Camlp4Parsers/Camlp4OCamlParser.cmo Camlp4Printers/Camlp4AutoPrinter.cmo
> Camlp4Bin.cmo pa_tryfinally.ml -o pa_tryfinally

Why link, with "-c" it's a lot simpler.

ocamlc -c -dtypes -pp camlp4of -I +camlp4 pa_tryfinally.ml

Cheers,

-- 
Nicolas Pouillard

Re: [Caml-list] try .. finally using new camlp4

[Bruno De Fraine]

On 09 Jul 2007, at 15:06, Nicolas Pouillard wrote:
> Let's go

Of course, if you wrote the thing, it's easy... :-)

>>   EXTEND Gram
>>     expr: LEVEL "top"
>>     [[ "try"; f=expr; "finally"; g=expr ->
> Here one extend a rule. So in order to have something working properly
> one *must* look at the original rule.
>
> There is the up-to-date rule:
>
> $ cvs ann -r release310
> camlp4/Camlp4Parsers/Camlp4OCamlRevisedParser.ml | grep '"try"'
> Annotations for camlp4/Camlp4Parsers/Camlp4OCamlRevisedParser.ml
> ***************
> 1.2.2.11     (pouillar 04-Apr-07):         | "try"; e = sequence;
> "with"; a = match_case ->
>
> So the correct rule is:
>     [[ "try"; f=sequence; "finally"; g=expr ->

Just a remark, you don't need the source code to check the existing  
definition.

$ ocaml camlp4orf.cma
# open Camlp4.PreCast ;;
# Gram.Entry.print Format.std_formatter Syntax.expr ;;

Will show:

expr: [
...
| "top" RIGHTA [
...
   | "try"; sequence; "with"; match_case

Regards,
Bruno

--
Bruno De Fraine
Vrije Universiteit Brussel
Faculty of Applied Sciences, DINF - SSEL
Room 4K208, Pleinlaan 2, B-1050 Brussels
tel: +32 (0)2 629 29 75
fax: +32 (0)2 629 28 70
e-mail: Bruno.De.Fraine@vub.ac.be

Re: [Caml-list] try .. finally using new camlp4

[Nicolas Pouillard]

On 7/10/07, Bruno De Fraine <Bruno.De.Fraine@vub.ac.be> wrote:
> On 09 Jul 2007, at 15:06, Nicolas Pouillard wrote:

[...]

> Just a remark, you don't need the source code to check the existing
> definition.

Good remark, thanks for adding it.

-- 
Nicolas Pouillard