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From: Atle <trollet@skynet.be>
Newsgroups: comp.lang.beta
Subject: Re: program 'cat.bet': Suggested implementation?
Date: Tue, 20 Jun 2000 14:59:11 -0100
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Xref: news.cs.au.dk comp.lang.beta:12456

Jorgen Lindskov Knudsen wrote:
> 
> 
> 
> The correct program part is:
> 
>    fil: @file(# accesserror:: (# do false->OK #);
>                 nosucherror:: (# do false->OK #);
>                 othererror:: (# do false->OK #);
>              #);
>    ...
>    true->OK;
>    fil. openread;
>    ...
Now, I tried experimenting with this, adding statements to the exception.
 
    fil: @file(# accesserror:: (# do false->OK #);
                 noSuchFileError:: (# do false->OK; true->continue #);
                 othererror:: (# do false->OK #);
              #);
	...
	true->OK;
	fil. openread;
    	if ( NOT OK then ' error' -> putLine; leave showFile if);
	...

so fra, OK. Calling betcat (I call the program betcat to not confuse with the operating system cat,
had some weird 'bugs' :-)

like this is OK, assuming betcat.bet exists and ls.bet does not:

$betcat betcat.bet ls.bet
 error
$

Now, let us say I want the specific error:
access error
no such file error
other error 

and so on. i did this:

    fil: @file(# accesserror:: (# do false->OK; true->continue; 'Access' -> putText #);
                 noSuchFileError:: (# do false->OK; true->continue; 'No such file' -> putText #);
                 othererror:: (# do false->OK; true ->continue; 'Other' ->putText #);
              #);
	...
	true->OK;
	fil. openread;
    	if ( NOT OK then ' error' -> putLine; leave showFile if);
	...

The program logic would the suggest this:

$betcat betcat.bet ls.bet
No such file error
$

However, it says 'reference is none' and i guess educatedly :-) that is is the 'No such file' string which is none. But I am raised
to believe that a '' delimited string can never be none, because it is a constant. 
What are the restrictions on which objects are valid in an exception?
Or did i do something else wrong?

Thanks, Atle