Eliminating upgrade risk

[Terry Reedy]

"John Roth" <johnroth at ameritech.net> wrote in message
news:tm3298o5hut5d1 at news.supernews.com...
 > [IBM] where installing a new version of the operating system, major
utilities
> and language processors was essentially **guaranteed** not to break
> running applications.

Ahem.  The way I learned the difference between call by reference and
call by value (about 1980) is when IBM Fortran, a major utility by any
standard, switched from one to the other while upgrading from Fortran
IV to Fortran 77(?) and my working code mysteriously quit working.  No
two-year transition period with warnings.  No option to keep the old
code working.  Just reread the revised manual, debug, and correct.  I
am very sure that this code breakage was not unique.  Certainly, they
were constantly revising the manuals.  (Oh, the days of having to
manually insert revision pages.  Is that why they called them
manuals?)Perhaps competition has pushed them to develop a new selling
point.

Terry J. Reedy