CORRECTION Re: Collective response to := messages

[dsr@hector.UUCP (David S. Rosenblum)]

In article <10906@ulysses.homer.nj.att.com> dsr@hector.UUCP (David S. Rosenblum) BLEW it!:
|
|In order to enforce this [evenness] constraint
|consistently in the manner of Ada, I would want to do the following:
|
|(1) Overload := so that it raises CONSTRAINT_ERROR when given an odd
|    right-hand-side.
|(2) Overload the attributes 'SUCC and 'PRED so that they skip odd values.
|(3) Overload the attributes 'POS and 'VAL so that count only even values.
|(4) Overload the attribute 'FIRST so that it returns the smallest even
|    value of EVEN's base type.
|(5) Overload the attribute 'LAST so that it returns the largest even
|    value of EVEN's base type.
|(6) Overload the membership tests and the ".." token so that only
|    even ranges are considered.
|(7) Overload the indexing operation for all array types I define that are
|    indexed by EVEN values, so that even-numbered components are stored and
|    accessed contiguously.
|(8) Overload the aggregate operation for such array types so that
|    the index values for the aggregate are computed "the right way".
|
|Yet after all these exertions, my evenness constraint would STILL not
|be enforced consistently, unless I was given several more language changes.
|For example, type conversions, qualifications, attribute evaluations and
|membership tests never propagate exceptions.

Oops, type conversions and qualifications CAN propagate exceptions,
so add the following to the above list:

(9)  Overload type conversion on EVEN so that CONSTRAINT_ERROR will be
     raised by an attempt to convert an odd value.
(10) Overload qualification on EVEN so that CONSTRAINT_ERROR will be
     raised by an attempt to qualify an odd value.

The rest of my message stands as written.


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