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From: steve@dim.sm.unisys.com (Steven Holtsberg)
Newsgroups: comp.lang.ada
Subject: Re: Implicit conversion?
Keywords: 11.6
Message-ID: <5737@sdcrdcf.sm.unisys.com>
Date: 13 Mar 89 22:31:53 GMT
References: <5678@sdcrdcf.sm.unisys.com> <46125@linus.UUCP>
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Reply-To: steve@sm.unisys.com (Steven Holtsberg)
Organization: Unisys Santa Monica
List-Id: <comp.lang.ada>


In article <46125@linus.UUCP> eachus@mbunix.mitre.org (Robert I. Eachus) writes:
>>procedure example is
>>  x: tiny_integer;
>>begin
>>  x:= MAX_INT - MAX_INT;
>>end example;
|
|     ... there is an implicit conversion of MAX_INT to tiny_integer.
|
|      ... but it is not converting the result to zero, it is using
| the "-" operator for tiny_integer and doing the conversion first.
| This is legal, and must be legal, on all implementations.  However,
| it may raise an exception during execution.  The reason Verdix
| doesn't raise CONSTRAINT_ERROR or NUMERIC_ERROR is more subtile.

I do not see how MAX_INT, (2147483647 in this implementation) can be
converted to TINY_INTEGER (-128 .. 127).  I believe that
the "-" operator for TINY_INTEGER is doing what 11.6(6) allows it to do,
that is, "...use the operation of a type that has a range wider that that of
the base type of the operands..."

| In 11.6(3) (but read
| all of 11.6) "...freedom is left to an implementation for reordering
| actions...that are...basic operations other than assignments.  This
| freedom is left, as defined below, even where the execution...may
| propagate a predefined exception."

I don't understand what freedom to reorder actions has to do with this example.