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[Caml-list] Re: OCAML Downcasting?
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Date: -- (:)
From: sejourne_kevin <sejourne_kevin@y...>
Subject: Re: [Caml-list] Re: OCAML Downcasting?
Marcin 'Qrczak' Kowalczyk wrote:
> skaller <skaller@users.sourceforge.net> writes:
> 
> 
>>>Attempts to avoid downcasts are often unmodular, they require to
>>>specify all possible variants in one place.
>>
>>It makes no difference. You have do specify them all anyhow,
>>downcast or not.
> 
> 
> It makes a difference because specifying them at the type definition
> would introduce a dependency loop between modules. And it would be
> unmodular: it would require changing some base module whenever a far
> client module is added.
> 
> Apply this reasoning to the exn type. Why don't you define all exn
> constructors in one place?

I think there is no problems with exceptions. But if you have problems 
managing exceptions in large modules have you try something like this ?

here an example:
I define all my exceptions like this :

let errors = ref [];;

(*to define an error*)
(*errors     "the exception" , the new value*)
errors :=   ("div by zero"   ,0)              :: (!errors);;

And the functions catch errors in this way:
let truc () =
   try
     ...
   with
      ... all Ocaml pre-defined exceptions
     | exn -> (* my exceptions in  errors list ref *)
	let s = Printexc.to_string exn in
	  ... Lex & Parse 's' in (fst errors) ref list , then handle error ...
;;

If exceptions are complex I can use polymorphic variants
for the "new value".

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