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[Caml-list] PXP
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Date: 2002-06-04 (22:53)
From: Gerd Stolpmann <info@g...>
Subject: Re: [Caml-list] PXP

On 2002.06.04 18:19 Gaurav Chanda wrote:
> Hello
> I am using PXP to parse and validate an XML document. The follwing code 	
> <?xml version="1.0"?>
> <methodCall>
>   <methodName>examples.getStateName</methodName>
>   <params>
>     <param>
>       <value><i4>41</i4></value>
>       </param>
>     </params>
>   </methodCall>
> gave this error at runtime: 
>   Fatal error: exception Pxp_types.At("In entity [toplevel] = ANONYMOUS, at line 2, position 12:", _)
> Could anybody help me solve this problem ?

In addition to Stefano's answer: Unfortunately, you do not get the full error message. 
This is an annoying problem of the runtime environment. Try the following code in the 

# raise(At("x",WF_error "y"));;
Exception: Pxp_types.At ("x", Pxp_types.WF_error "y").
# try raise(At("x",WF_error "y")) with any -> Failure(Printexc.to_string any);;
- : exn = Failure "Pxp_types.At(_)"
If you compile raise(At("x",WF_error "y")), and start the program, you get a third 

Fatal error: exception Pxp_types.At("x", _)

There are three different built-in routines to print uncaught exceptions, and all three
have different capabilitites, and only one can print nested exceptions.

The workaround for PXP is to use the special exception printer Pxp_types.string_of_exn

  <your code raising the exception>
  error ->
    failwith(Pxp_types.string_of_exn error)

and you get always an exception that can be printed, regardless which printer happens
to catch the exception.

Gerd Stolpmann      Telefon: +49 6151 997705 (privat)
Viktoriastr. 45             
64293 Darmstadt     EMail:   gerd@gerd-stolpmann.de
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