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From: lewbloch <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Call by Result
Date: Wed, 15 Jun 2011 07:06:47 -0700 (PDT)
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On Jun 14, 2:18=A0pm, Andreas Leitgeb <a...@gamma.logic.tuwien.ac.at>
wrote:
> Arved Sandstrom <asandstrom3min...@eastlink.ca> wrote:
> > It's way more concise than Java, and another advantage still remains
> > that we're not looking for a special value (null).
>
> I'm not yet sure, whether null in Java counts as a "String value", or not=
.
>
> I think it is not (whereas the empty string of course is). As such, a
> variable (or field) "s" (or even an expression) of type String really
> happens to be implicitly the pendant of Haskell's "Option"al String:
>
> Either it is "Null"... (ahem, "null"), or it holds an actual String value=
.
>
> Ditto for all the non-primitive types.

'null' is an out-of-band 'String' value (or any other reference type).

I use the "is-a {type}" to indicate if assignment (or casting) is
permissible.  'String x =3D null;' is valid, so 'null' is a 'String' (or
any other reference type) value.  It is "out of band", which expresses
the "not-a" concept well enough to write good software.

--
Lew