"Substantive Changes" (was: OO COBOL - What if ???

"LX-i" <lxi0007@netscape.net> wrote in message
 news:GIqdnW9gzIumOJTanZ2dnUVZ_oKhnZ2d@co
mcast.com...
> Clark F Morris wrote: 
<snip>
> And, regarding your last comment - which constructs gave different behavio
r
> with the same syntax?  I'll agree with you on that point - that's not a go
od
> thing.
>

Each Standard (or at least all the ones that I know about - I have never
"studied" the '68 and only glanced at an "offical" '74) includes a  section
called

"Substantive Changes potentially affecting existing programs"

These DO include cases where "old syntax" can give "new results".  Usually t
hese
are due to interpretation requests (usually places where the old standard di
dn't
say what people wanted/expected).

One example, in the '02 Standard was what a program needed to do if a divide
 by
zero occured in an arithmetic statement and no "ON SIZE ERROR" phrase was
specified.  By "mistake" (according to many) the '85 Standard was interprete
d as
REQUIRING a conforming implementation to "silently continue" on after such
statements.  Many implementations had "always" ABENDed or "abnormally
terminated" at such times. The '02 Standard changed the wording to ALLOW thi
s to
happen in a conforming implementation - but this was a change from the previ
ous
Standard.

The classic example between the '68 and '74 Standard was how to interprete
certain combined abrreviated expressions with NOT in them, e.g.
A = B AND NOT LESS THAN C OR D

in the '68 Standard was equivalent to
((A = B) AND NOT (A < C) OR (A < D))

in the '74 (and later) standards it is equivalent to
((A = B) AND (A NOT < C) OR (A NOT < D))

I won't go into the history of how/why this happened, but this is the type o
f
thing that DOES happen between Standards - and that is "so documented".



--
Bill Klein
wmklein <at> ix.netcom.com