Bug in ocamlc or in ocamlrun.

Bug in ocamlc or in ocamlrun.

[Marc Lasson]

Hello,

When i compile the following program with ocamlc i get a segmentation fault. 

Is it a bug in the ocaml system ? I did not succeed to isolate it.
                                 ----------------------
module LL (R : sig
 type t
 val add : t -> t -> t
end) =
 struct
   type t = R.t list
   let add = List.map2 (R.add)
 end

module rec M : sig
   type t = P of int | L of LS.t
   val add : t -> t -> t
   val to_string : t -> string
 end = struct
   type param = ()
   type t = P of int
               | L of LS.t
             let add a b = match a, b with
     P a', P b' -> P (a'+b')
   | L a', L b' -> L (LS.add a' b')
   | _ -> failwith "incompatible"

   let rec to_string = function
      P i -> string_of_int i
    | L l -> List.fold_left (fun r x -> r^" "^(to_string x)) "" l
 end
and LS : sig type t = M.t list val add : t -> t -> t end = LL(M)

open M
let p = L [P 1; P 2]
let q = add p p
let () =
 print_endline (to_string p);
 print_endline (to_string q)
                                 ----------------------

If i replace the function LL.add by

 let rec add a b = match a, b with
     [], [] -> []
   | x::a', y::b' -> (R.add x y)::(add a' b')
   | _ -> failwith "add"

the segmentation fault magically disappear.

Hope that helps,
-- 
Marc Lasson.

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Jonathan Roewen]

Interesting.

I pasted into a toplevel (3.09.0), and it died with the message:

>> Fatal error: Primitive update_mod not found.
Fatal error: exception Misc.Fatal_error

That might be the cause...

Jonathan

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Keiko Nakata]

From: Marc Lasson <titmarc@free.fr>
Subject: [Caml-list] Bug in ocamlc or in ocamlrun.
Date: Wed, 19 Apr 2006 01:16:27 +0200

> When i compile the following program with ocamlc i get a segmentation fault. 
> 
> Is it a bug in the ocaml system ? I did not succeed to isolate it.
>                                  ----------------------
> module LL (R : sig
>  type t
>  val add : t -> t -> t
> end) =
>  struct
>    type t = R.t list
>    let add = List.map2 (R.add)
>  end
> 
> module rec M : sig
>    type t = P of int | L of LS.t
>    val add : t -> t -> t
>    val to_string : t -> string
>  end = struct
>    type param = ()
>    type t = P of int
>                | L of LS.t
>              let add a b = match a, b with
>      P a', P b' -> P (a'+b')
>    | L a', L b' -> L (LS.add a' b')
>    | _ -> failwith "incompatible"
> 
>    let rec to_string = function
>       P i -> string_of_int i
>     | L l -> List.fold_left (fun r x -> r^" "^(to_string x)) "" l
>  end
> and LS : sig type t = M.t list val add : t -> t -> t end = LL(M)
> 
> open M
> let p = L [P 1; P 2]
> let q = add p p
> let () =
>  print_endline (to_string p);
>  print_endline (to_string q)


Strangely, OCaml version 3.08.0 can handle this code.
So, the developer team must know the reason.
Did you write a bug report ?

Keiko NAKATA

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Marc Lasson]

Keiko Nakata wrote:

>Strangely, OCaml version 3.08.0 can handle this code.
>So, the developer team must know the reason.
>Did you write a bug report ?
>  
>
According to <http://caml.inria.fr/pub/distrib/ocaml-3.09/notes/Changes>,
there was a change about recursive modules. They may have add a bug.

> Did you write a bug report ?
>
Hum. Should I ?
I am not expert at all, i have never written any bug report.
I don't know many things about ocaml sources.

-- 
Marc Lasson.

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Remi Vanicat]

2006/4/19, Marc Lasson <titmarc@free.fr>:
> Keiko Nakata wrote:
>
> >Strangely, OCaml version 3.08.0 can handle this code.
> >So, the developer team must know the reason.
> >Did you write a bug report ?
> >
> >
> According to <http://caml.inria.fr/pub/distrib/ocaml-3.09/notes/Changes>,
> there was a change about recursive modules. They may have add a bug.
>
> > Did you write a bug report ?
> >
> Hum. Should I ?

Yes, please do. The member of the ocaml teams don't read all message
here, but they read all bug report

> I am not expert at all, i have never written any bug report.

Just give the example telling what happen

> I don't know many things about ocaml sources.

You don't need to to send bug report. Bug report only state problems,
and the ocaml team will ask for further information if it's needed

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Sebastian Egner]

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> When i compile the following program with ocamlc i get a segmentation 
fault. 
> [...]
> If i replace the function LL.add by
> 
>  let rec add a b = match a, b with
>      [], [] -> []
>    | x::a', y::b' -> (R.add x y)::(add a' b')
>    | _ -> failwith "add"
> 
> the segmentation fault magically disappear.

It seems that it is sufficient to define

        let add a b = List.map2 R.add a b

instead of

        let add = List.map2 R.add

to make the segmentation fault disappear (Ocaml 3.09.1).

Sebastian.

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Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Jonathan Roewen]

> It seems that it is sufficient to define
>
>         let add a b = List.map2 R.add a b
>
> instead of
>
>         let add = List.map2 R.add
>
> to make the segmentation fault disappear (Ocaml 3.09.1).

That is besides the point =P The fact is that the code -does- segfault
while there is nothing syntactically (and probably semanticly) wrong
with the code.

Jonathan

Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Sebastian Egner]

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Besides the point or not, here is a much simpler version of
Marc's program which also segfaults (ocamlc 3.09.1), and 
probably due to the same reason:

---

module type Aut =
  sig 
    type t 
    val f : t -> t 
  end

module Map(A : Aut) =
  struct
    type t = A.t list
    let f = List.map A.f (* => Segmentation fault *)
(*  let f x = List.map A.f x *) (* => Stack overflow (correct) *)
  end

module rec M : (Aut with type t = int) =
  struct
    type t
    let f x = 
      match MapM.f [x] with 
      | [y] -> y 
      | _   -> assert false
  end
and MapM : (Aut with type t = M.t list) = 
  Map(M)

open M;;
M.f 0

---

Sebastian

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Re: [Caml-list] Bug in ocamlc or in ocamlrun.

[Alain Frisch]

Sebastian Egner wrote:
> Besides the point or not, here is a much simpler version of
> Marc's program which also segfaults (ocamlc 3.09.1), and
> probably due to the same reason:

And here's yet a simpler one:
module rec M : (sig val f : int list -> int list end) =
struct let f = List.map succ end
let _ = M.f []

I've submitted a bug report.

-- Alain