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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Q: unboxed values and polymorphism
Date: 1996/06/18
Message-ID: <dewar.835121144@schonberg>#1/1
X-Deja-AN: 161541341
references: <uvv7mt7ubgd.fsf@chaq.informatik.uni-tuebingen.de>
 	<Dt4FCx.29H.0.-s@inmet.camb.inmet.com>
 <uvvwx1661tz.fsf@chaq.informatik.uni-tuebingen.de>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-06-18T00:00:00+00:00
List-Id: <comp.lang.ada>


Hannes says

"But will this give me unboxed integers and type information on the stack ?
I'd try a private type that's actually an integer. I'd use half of this
integers (-2**30 ... 2**30-1) for my fixnums. Values outside this range
would be indices in arrays of bignums or list cells. So I'd have unboxed
integers and type information on the stack."

You are encoding at a very low level, appropriate for C (since it is the
only way to do things), but totally inappropriate for Ada. You need a
variant record with a discriinant to indicate whether you have fixnums
or indices. The discriminant would be a single bit.