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From: mgushee@havenrock.com
To: caml-list@pauillac.inria.fr
Date: Tue, 11 Mar 2003 20:43:26 -0700
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Subject: RE: [Caml-list] Checked exceptions and type inference
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On 11 Mar 2003 at 22:00, Arturo Borquez wrote:

> Brian Hurt <brian.hurt@qlogic.com> wrote:

> >Java treats checked exceptions as part of the type signature of the
> >function.  As such, it seems to me that as such, type inference would work
> >to propogate most of this information in a more convient way.

>  let x = try String.sub str pos len with _ -> "" in
>  ....
> 
> in this case failing String.sub is returning a string,
> and the type inference system will check it that way.
> 
> Perhaps I don't understand what migth be a
> 'checked exception' in ML. I am missing something?.
> can you explain it with an example?

I guess you must be unfamiliar with Java terminology. A checked 
exception is one that the programmer must provide for in any method 
that can raise it, either by writing a handler or by indicating in 
the method signature that the method may raise that exception. 
They're called "checked" because the compiler checks whether they are 
handled. For example, if you have a method getConfig() that reads a 
configuration file, you have to provide for possible I/O errors: 
either

    try {
        /* open and read file */
    } catch (IOException e) {
        /* handle exception */
    }

Within the body of the method, or a signature such as:

    public HashTable getConfig() throws IOException {
        /* do whatever */
    }

so in the latter case, the exception is indeed part of the method 
signature.

Unchecked exceptions are generally those resulting from unpredictable 
conditions, such as OutOfMemoryError, NullPointerException, and 
ThreadDeath.

--
Matt Gushee
Englewood, CO USA

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