Re: [BLACKBOX] Variable initialization in BlackBox

From: [at]} <Chris>
Date: Fri, 10 Oct 2008 11:26:04 +1030

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>
>>> -----Original Message-----
>>> From: Alexander Iljin [mailto:ajsoft{([at]})nowhere.xy
>>> Sent: 09 October 2008 10:21
>>> To: BlackBox
>>> Cc: Campbell, Robert (SELEX GALILEO, UK)
>>> Subject: Re: [BLACKBOX] FW: [BLACKBOX] Variable initialization in
>>> BlackBox
>
>>>
>>> I think the report is ambiguous in one respect. I does state what
>>> is
>>> initialized and when, but it does not explicitly state whether the
>>> unmentioned items are initialized (e.g. it does not say that local
>>> INTEGERs may or may not have random values).
>>>

Note that the Report states in the introduction:

"This report is not intended as a programmer's tutorial. It is intentionally
kept concise. Its function is to serve as a reference for programmers. What
remains unsaid is mostly left so intentionally, either because it can be
derived from stated rules of the language, or because it would require to
commit the definition when a general commitment appears as unwise."

Basically if the report does not provide an answer a question on a
particular issue then you should not rely on any assumption. Another example
is:

CHR(x) integer type CHAR character with ordinal number

What if x is negative? The behaviour is not specified. Consequently if you
want predictable behaviour then you have to ensure that x is not negative.

Attempts at clarification can often lead to more problems e.g. if the report
were to specify that local variables will have random values then the CP
implementor would then have to *ensure* that they had random values. What is
a 'random' value?

If you are interested in previous attempts to achieve unambiguous watertight
language definitions see:

"Some reflections on Modula-2 standardization"

http://www.scifac.ru.ac.za/cspt/sc22wg13.htm

(Warning: it is painful)

Somehow the eminently readable 25 page Modula-2 Report turned into a
virtually incomprehensible document with more than 500 pages!

Regards,
Chris Burrows

Armaide: Oberon-07 Development System for ARM processors
 http://www.armaide.com




 

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Received on Fri Oct 10 2008 - 02:56:04 UTC