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Line number for index out of bounds
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Date: -- (:)
From: Andries Hekstra <andries.hekstra@p...>
Subject: Re: [Caml-list] Line number for index out of bounds / Exceptions for left hand side of assignments
Richard Jones wrote :
> Possible workarounds:
> ...
> * Surround every possible array index with a try ... with expression
> like this:
> 
>   try
>     (* code which accesses the array *)
>   with
>     Invalid_argument "index out of bounds" -> assert false
> 
> The "assert false" will print the line and character number of the
> assertion.

Dear Richard,

I agree with you that this is feasible whenever array elements feature in 
the right hand side of assignments. But how about the left hand sides of 
assignments ? E.g. the following obviously is not correct OCaml syntax.

        let a = Array.init 2 0;;

        try a.(2) <- 1
          with
            Invalid_argument "index out of bounds" -> assert false;;

        let h = try a.(2)
           with
            Invalid_argument "index out of bounds" -> assert false in
            h <- 1;;

Regards,

=Andries

------------------------------------------------------------------------
Dr. Ir. Andries P. Hekstra
Philips Research 
High Tech Campus 27  (WL-1-4.15)
5656 AG Eindhoven
Tel./Fax/Secr. +31 40 27 42048/42566/44051 
   *  Good open source break software for computer users : 
http://www.workrave.org 








Richard Jones <rich@annexia.org> 
06-03-2006 12:14

To
Andries Hekstra/EHV/RESEARCH/PHILIPS@PHILIPS
cc
caml-list@yquem.inria.fr
Subject
Re: [Caml-list] Line number for index out of bounds
Classification







On Mon, Mar 06, 2006 at 11:44:31AM +0100, Andries Hekstra wrote:
> Invalid_argument("index out of bounds")
[...]
> Of course, I am very curious in which line number of the program this 
> exception occurs. 
> Is there any way to get hold of this line number?

This is a real problem with OCaml - it's impossible to get stack
traces of where an exception happens with native code.  I'm assuming
you're using native code.  I commonly have cases where a program dies
with "exception: Not_found" because I forgot to enclose some List.find
with an appropriate try ... with clause, or made some wrong
assumption.  Tracking these down is time-consuming.

Possible workarounds:

* Use bytecode, and before running the program set the environment
variable OCAMLRUNPARAM=b which will print a stack trace.

* Surround every possible array index with a try ... with expression
like this:

  try
    (* code which accesses the array *)
  with
    Invalid_argument "index out of bounds" -> assert false

The "assert false" will print the line and character number of the
assertion.

* Hack ocamlopt to be able to print exceptions properly :-)

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
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