On Sun, 05 Mar 2000 19:00:57 GMT, "James Giles"
<jamesgi...@worldnet.att.net> wrote:The first system to systematically chase undefined variables that I am
>netnet wrote in message <38C22FA6.89C90...@netnetnet.net>...
>>I'm not inventing new terminology here, it's just 'misspelling', read: uninitialized
>The two are not synonyms. An unitialized variable is not necessarily
aware of was WatFor for IBM 7040's. It used a cheat as it deliberately
stored bad parity into memory and then declared that all bad parity
references were for use of undefined variables. So on the exceedingly
rare case of a real bad parity you could be a bit confused. Other than
that you will read the fine print and find that there is a forbidden
value which is declared to be off limits. The bad parity check was a
thirty line assembly hack. The forbidden value scheme is a lot of work
as even the WatFor folks found out when they tried to replicate their
very good feature on IBM 360/xx's back when xx was still small like
50. So if you are using character data for other than printable and
other defined characters you have a risk of finding out about the fine
print that you may never have examined carefully. For systems without
NaNs for floating there are usually an adequate supply of otherwise
illegal configurations, logical is only supposed to have two states
(before vendor extensions) under control of the system and integers
cause the forbidden value to be a bother. This is particularly true if
the user and the system implementors have similar notions of
distinctive flag values.
None of which lessens the need for or utility of IMPLICIT NONE. I am
>For most implementations, *any* bit pattern is a legal value for thoseUnfortunately some of the systems that implement undefined variable
>You seem to be under the impression that identifying an unitialized
checking seem to treat the setting of an undefined variable in some
circumstances in a subroutine as an error according to their current
implementations. (They act as if one must reference it before setting
it in those curious circunstances!) They agree that such treatment is
in fact a bug but the fix seems a bit slow in coming. I do not know
the sorry internal details of the bug but it appears that this is in
fact a side effect of some other problem. Either way as a user I am
less than pleased, as the unnamed vendor knows rather well from the
apologies from their senior folks. One of the downsides of undefined
variable chacking is that it makes the system larger with all the
attendent bothers. The checklist purchasing which seems to greatly
value optimizations and to give zero credit for good debugging
facilities is not going to get a lot of good debugging support
developed. Bob Runyan's notion that diferent systems should be given
credit for differing strengths so much that one routinely uses several
systems has a lot going for it.
Poor implementation of a good idea is not directly an arguement
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