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From: Dave Berry <dave@kal.com>
To: Hongwei  Xi <hwxi@ececs.uc.edu>, caml-list@inria.fr
Subject: RE: reference initialization
Date: Thu, 11 May 2000 14:48:02 +0100
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IMO, the "ML strategy" is to use an option type.  SML has 
	datatype 'a option = NONE | SOME of 'a
although I prefer 
	datatype 'a option = NULL | VALUE of 'a.
I don't know if Caml provides such a type as standard, although
it's easy to define your own.

Then your code checks whether the value has been assigned (dynamically,
as you require), and can take whatever action is appropriate.  If you want
to throw an exception, you can.

With this approach, the ML type system tells you which values may be null.
This has an advantage over the Java approach, where any value may be
null or uninitialised.

Dave.

-----Original Message-----
From: Hongwei Xi [mailto:hwxi@ececs.uc.edu]
Sent: Wednesday, May 10, 2000 5:50 AM
To: caml-list@inria.fr
Subject: reference initialization


> Wrong. You have references, which are quite better than pointers
> (they are typed, and necessarily initialized)

Suppose I use a reference 'x'. If I know what the initial value
of 'x' should be, I'll of course prefer to initialize it with that
value. Now suppose I don't, that is, I intend to assign a value
to 'v' later (maybe in a loop or in a conditional branch)

(1) ML strategy: initialize x with any value 'v' of an appropriate
type (sometimes, such a 'v' is difficult to find or takes time to
construct (consider 'x' to be a large array)).