Thomas Chust scripsit:
> this is really a question of taste, isn't it? You could just as well argue
> that a NULL value should be of a type that is a subtype of every other
> existing type but contains no other concrete instances, which would imply
> that all the type predicates should return #t when applied to the NULL
> value. This makes a lot of sense when the NULL value is used to indicate
> the absence of an object reference and is the way it is handled in several
> object oriented languages.
As far as I know, no OO language does that. They interpret (or IMHO
misinterpret) a *static* declaration that a variable is of type Foo
as meaning that it can contain a Foo or null, but nowhere is null
*dynamically* a member of type Foo: tests analogous to number?, string?,
etc. always return false on null.
Haskell spells it out: a foo-typed variable can only hold a foo, and if
you want it to be otherwise, you declare it as of type Maybe foo, which
means it can hold either a Just foo (which you can unwrap to be a foo)
or Nothing.
OT: One of the Java puzzlers is this:
Foo foo = null;
foo.bar();
Under what circumstances does that *not* cause a NullPointerException?
--
We are lost, lost. No name, no business, no Precious, nothing. Only empty.
Only hungry: yes, we are hungry. A few little fishes, nassty bony little
fishes, for a poor creature, and they say death. So wise they are; so just,
so very just. --Gollum [EMAIL PROTECTED] http://ccil.org/~cowan
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