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From: Jeffrey Carter <jeffrey.carter@boeing.com>
Subject: Re: an infinate loop
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Ted Dennison wrote:
> 
> For another, most of your "exit" statements are all at the tops of the loops. In
> those cases you should probably reverse the test logic and use "while" loops
> instead.

This is bad advice. The form that uses positive logic is best.

exit when End_Of_File;

uses positive logic, and is better than

while not End_Of_File loop

which uses negative logic. All of the exits in this program use positive
logic. In general, exit tends to use positive logic and while tends to
use negative logic.

However, when exiting from nested loops, it is a good idea to name your
loops and use the loop names on the exit statements and the end loop
statements. This badly formatted program is hard enough to understand
without trying to figure out which end loop corresponds to which exit.

At the "Ada Launch" (1980 Dec 10), Ichbiah, Barnes, and Firth introduced
the recently renamed Ada language (MIL-STD 1815, formerly Green, now
known as Ada 80) to the world. They said "while" was in the language
primarily to support translation from languages such as Pascal, and
advised using the "loop ... exit when" format in new code.

-- 
Jeffrey Carter