Path: utzoo!attcan!uunet!cs.utexas.edu!rice!titan.rice.edu!rama
From: rama@titan.rice.edu (Ramarao Kanneganti)
Newsgroups: comp.lang.functional
Subject: Re: Can laziness sometimes be too lazy?
Summary: Error > bottom
Keywords: Domains as information systems, bottom, error
Message-ID: <10268@brazos.Rice.edu>
Date: 26 Jul 90 15:55:47 GMT
References: <2706@bruce.cs.monash.OZ.AU> <3188@osc.COM> <3926@rex.cs.tulane.edu>
Sender: root@rice.edu
Organization: Rice University, Houston
Lines: 30

In article <3926@rex.cs.tulane.edu> fs@rex.cs.tulane.edu (Frank Silbermann) writes:
>If you "handle" an exception then it is no longer an error
>-- just another possible result.  Semantically speaking,
>an error is an _unhandled_ exception.  Since it is unhandled,
>why not declare the result to be `undefined' (i.e. is bottom)?

Error is much more than bottom. Bottom is least informative. If you
sitting in front of a terminal you notice when the program doesn't
come back with any thing, or if it comes back with an error message.
Error is more informative than bottom. Would you equate abort(5) with
bottom, simply because abort is unhandled?

>
>Make an analogy with mathamatics.  Consider the function f(x) = 5/x.
>What is the value of the function at x=0?  `Error' or `undefined'?
>

It can be a matter of choice of how you define the function f. But, if
you want to give maximal information, it should be error.  Suppose you
have a domain with a chain like, a <= b <= c. After getting the result
b, in the further query, you get an error. Do you still call the
result b? I claim that it is an error element, and it is above b. But
any function which is strict in bottom is also strict in error, so any
choice will be consistent.


>	Frank Silbermann	fs@rex.cs.tulane.edu

	thanks,
	Ramarao Kanneganti	rama@rice.edu