[Haskell-cafe] Re: Laws and partial values

[Conal Elliott]

On Sun, Jan 25, 2009 at 1:08 AM, Daniel Fischer <daniel.is.fischer at web.de>wrote:

> Am Sonntag, 25. Januar 2009 00:55 schrieb Conal Elliott:
> > > It's obvious because () is a defined value, while bottom is not - per
> > > definitionem.
> >
> > I wonder if this argument is circular.
> >
> > I'm not aware of "defined" and "not defined" as more than informal terms.
>
> They are informal. I could've written one is a terminating computation
> while
> the other is not.

> Which definition(s) are you referring to?
> >
> >   - Conal
>

I think I smell the same sort of circularity in this shifted "per
definitionem" argument as well.  Here's how I imagine making this implicit
argument explicit:

Define "terminating" (or undefined) to mean "/= _|_" and "not terminating"
(undefined) to mean "== _|_".  Then, since () is obviously terminating
(defined), it follows that () /= _|_ .

Is that the argument you had in mind?

Does anyone see the flaw in that logic (and hence the purpose of
"obviously").

   - Conal
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