[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: cheerful static typing (was: Any and Every... (was: Eval))
Date: Thu, 10 Jan 2002 12:49:25 -0500 (EST)
From: Dan Weinreb <firstname.lastname@example.org>
CC: email@example.com, firstname.lastname@example.org, email@example.com,
Subject: Re: cheerful static typing (was: Any and Every... (was: Eval))
Date: 10 Jan 2002 12:31:00 -0500
firstname.lastname@example.org (Gregory T. Sullivan) writes:
> Put another way, all programs, for given a static analysis, fall into
> one of three camps:
> (1) Statically safe - proven to be free of runtime errors.
This isn't necessarily the case. You can have a `statically safe'
program that `throws an exception' or `invokes the error handler' at
You should not equate "runtime error" with "throws an exception".
Some errors do not throw exceptions, and some throws of exceptions are
not errors. An error is when a program fails to meet its defined
contract. If you call integer divide on 2 and 0, and it throws a
zero-divide exception, that's not an error, because integer divide
is obeying its contract.
Careful, here, Dan; taking this to a logical extreme
implies that, if you beef up the contracts, you can
define away all errors.
Maybe we could say that a run-time error is a situation
in which a program exhibits one of a set of behaviors
that we choose to describe as "undesirable"? Often
throwing one of a certain set of exceptions is considered
undesirable; indeed, the division-by-zero exception may
be undesirable in some contexts despite the fact that
it's in the contract of the "/" operator.