From help-octave-request at bevo dot che dot wisc dot edu  Thu Jan 27 15:07:35 2000
Subject: Re: Suggestion:  add do-enddo(condition)
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 27 Jan 2000 15:08:03 -0600 (CST)

People have proposed

  1.      do ... enddo (condition)
  2.      do ... while (condition)
  3.      do ... until (condition)
  4.  repeat ... until (condition)

For completenes, I'll add

  5.  repeat ... while (condition)

Although it is consistent with the typical `foo ... endfoo' syntax of
Octave, I don't like 1 much because it is not clear to me whether the
loop runs while the condition is true or until it is true.  Both 3 and
4 are the same, as are 2 and 5, except for the keyword repeat vs. do.
I don't have a strong preference.

So, we are left with two cases, which you can currently implement
with

  do ... while (condition)  -->

    while (1)
      ...
      if (! condition) break endif
    endwhile

  do ... until (condition)  -->

    while (1)
      ...
      if (condition) break endif
    endwhile

but the new forms might be a little clearer.

Using while as a keyword to end loops as well as begin them does not
present a serious problem for the parser.

Note that since repeat or do and until would become keywords, they
would no longer be available as possible variable names, so that could
be a compatibility problem.

Implementing this would not be hard, if anyone is interested.

jwe



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