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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: DECAda/VMS - calling GETJPI
Date: 1996/06/05
Message-ID: <dewar.834000380@schonberg>#1/1
X-Deja-AN: 158644840
references: <31B2AF74.668E@dial.eunet.ch> <dewar.833897047@schonberg>
 <4p1v56$214@linus.mitre.org> <dewar.833924742@schonberg>
 <DsJ6vu.Ev6@world.std.com>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-06-05T00:00:00+00:00
List-Id: <comp.lang.ada>


The basic idea here is that type conversion converts the type, but not
the value, of course floating-point to int already violates this somewhat
as Bob points out, but not quite as dramatically.

Consider the following example:

    type x is mod 10;
    subtype y is x range 0 .. 5;

    vy : y;

    vy := y (-4) -- raises constraint error
    vy := y (-6) -- ok, gives result of 4

At the meeting we accumulated a series of odd examples of this kind, and
decided that it is just a bit too weird to have type conversion generating
what amounts to a significant arithmetic computation.

P.S. in my comments in the example above, I am assuming for the moment the
old semantics. In current Ada 95, BOTH assigments to vy raise constraint
error, since -1 is not in the range 0 .. 5.

Actually to be strict, the constraint error is raised by the conversion
because -1 is not in the set of values for modular type x (0 .. 10).