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Re: Exceptuations
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From:
Dave Whipp
Date:
October 5, 2005 13:40
Subject:
Re: Exceptuations
Message ID:
20051005204004.30882.qmail@lists.develooper.com
Luke Palmer wrote:
> Of course, exactly how this "public interface" is declared is quite undefined.
Reading this thread, I find myself wondering how a resumable exception
differs from a dynamically scropted function. Imagine this code:
sub FileNotWriteable( Str $filename ) {
die "can't write file: $filename";
}
sub write_file (Str $filename) {
FileNotWriteable($filename) unless -w $filename;
...
}
sub my_program {
temp sub FileNotWriteable( Str $filename ) {
return if chmod "+w", $filename;
OUTER::FileNotWriteable( $filename );
}
...
write_file("foo.txt");
...
}
Ignoring syntactic sugar, what semantics does exception handling have
that a dynamically scoped function does not?
In the case of non-resumable exceptions, we see things like deferred
handling -- the exception is passed as a property of an undef value. I
assume such an exception cannot be resumed, so it does appear to me that
there are fundamental differences between resumable things, and
non-resumable, deferrable, exceptions. What is the benefit of unifying
them under a common syntax (CATCH blocks)?
Larry suggested that the exception mechanism might be a way of unifying
errors and warnings; but perhaps the opposite is true. Perhaps what we
see is a needed to generalize the distinction between warnigns and errors.
Dave.
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