problem with camlp4

problem with camlp4

[Benedikt Grundmann]

Hi everybody,

I'm having a problem with a syntax extension I'm trying to write, the
smallest sample that I could come up with, that still shows the
problem is the following:

(*pp camlp4orf *)

open Camlp4.PreCast

let test _loc =
  let num = 0 in
  let acc = <:match_case<>> in
    (*
  <:match_case< true -> $expr:num$ | $acc$ >>
     *)
  <:match_case< true -> 0 | $acc$ >>

If I comment out the last line and instead enable the line above I get
this error:

ocamlc -c -pp "camlp4orf " -thread -g -I
/home/bene/godi/lib/ocaml/std-lib/camlp4 sample.ml
File "sample.ml", line 8, characters 23-25:
While expanding quotation "match_case" in a position of "expr":
  Parse error: "->" expected after [opt_when_expr] (in [match_case0])

I'm sure I missed something obvious... Please help.

Thanks a lot,

Bene


-- 
Calvin: I try to make everyone's day a little more
surreal.

(From Calvin & Hobbes)

Re: [Caml-list] problem with camlp4

[Jon Harrop]

On Monday 02 July 2007 23:04:18 Benedikt Grundmann wrote:
> I'm sure I missed something obvious... Please help.

I think you need to antiquote a quoted expression:

  open Camlp4.PreCast

  let test _loc =
    let acc = <:match_case<>> in
    <:match_case< true -> $<:expr<0>>$ | $acc$ >>

What does match_case do?

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

Re: [Caml-list] problem with camlp4

[Bruno De Fraine]

On 03 Jul 2007, at 00:04, Benedikt Grundmann wrote:

> <:match_case< true -> $expr:num$ | $acc$ >>

Do you mean this?

<:match_case< true -> $int:string_of_int num$ >>

Also notice that you can write
<:expr< match $e$ with [ $list:l$ ] >>
where l is of type "Camlp4.PreCast.Ast.match_case list".

This can be easier than folding the expression with an accumulator.

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] problem with camlp4

[Bruno De Fraine]

On 03 Jul 2007, at 07:46, I wrote:

> <:match_case< true -> $int:string_of_int num$ >>

Alain Frisch reminded me this can be shortened to

<:match_case< true -> $`int:num$ >>

with the new camlp4.

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] problem with camlp4

[Nicolas Pouillard]

On 7/3/07, Benedikt Grundmann <benedikt@cardexpert.net> wrote:
> Hi everybody,
>
> I'm having a problem with a syntax extension I'm trying to write, the
> smallest sample that I could come up with, that still shows the
> problem is the following:
>
> (*pp camlp4orf *)
>
> open Camlp4.PreCast
>
> let test _loc =
>   let num = 0 in
>   let acc = <:match_case<>> in
>     (*
>   <:match_case< true -> $expr:num$ | $acc$ >>
>      *)
>   <:match_case< true -> 0 | $acc$ >>
>
> If I comment out the last line and instead enable the line above I get
> this error:
>
> ocamlc -c -pp "camlp4orf " -thread -g -I
> /home/bene/godi/lib/ocaml/std-lib/camlp4 sample.ml
> File "sample.ml", line 8, characters 23-25:
> While expanding quotation "match_case" in a position of "expr":
>   Parse error: "->" expected after [opt_when_expr] (in [match_case0])

First, "expr" in $expr:...$ is not a valid antiquotation name,
(perhaps it should be) but here you can use $exp:...$ or even just
$...$ since it's not ambiguous that after the "->" one waits an
expression.

Second, you try to put an integer right here.
You need to make a expression node for it (as told by other answers):
- A constant can be put directly: <:expr< 0 >>
- A string expression representing an integer can be put like that:
<:expr< $int:"0"$ >>
- An integer expression can be used with this sugar: <:expr< $`int:0$ >>

The last but not the least, in revised <:match_case< true -> 0 >> is
nothing more than <:match_case< _ -> 0 >>. Since the true constant is
spelled True with a capital T like any other data constructor.

Cheers,

-- 
Nicolas Pouillard