RE: ILE RPG:Is the use of ITER & LEAVE Structured Programming?

Adding more fuel to the fire, Alexi said:

>At that time, after aggressive attacks on GOTO usage,  it was generally
>agreed that GOTO or similar operation is sometimes needed to make a
>complicated algorithm more readable and maintainable (there was
>classical paper about it by Knuth, if I remember it right). Since GOTO
>has become a taboo, ITERATE and LEAVE operations were introduced by some
>of the computer science gurus of the time (I do not remember the name).
>So, ITERATE and LEAVE operations ARE structured programming by
>definition. So real purist will have to accept it. Of course, they have
>every right to dislike them personally, but then they will no longer be
>purists.

My college days are fuzzy for a variety of reasons... but, the one thing I
do remember was that the major problem with GOTO was that it allowed the
programmer to exit a block of code unconditionally.  Unconditional branches
are not part of stuctured programming.

ITER and LEAVE fall into the unconditional branch catagory as well, and
that seems to be a major problem with their usage.  They tend to make the
code grow horizontally, promoting a monolithic structure.

Also, ITER and LEAVE are not self-documenting.  It may not be easy to see
why ITER is being used at this point, unless comments are included in the
code.

So, purists may argue with you on this point, Alexi.

But, as a practical matter, I've had a few discussions with a few folks
off-list regarding ITER/LEAVE and so forth, and the main thread that seems
to run through all the conversations has been-- "it's a tool, so if it's
used properly, it's OK".

I agree, but with serious reservations.  Namely, that while I may implement
ITER/LEAVE correctly... someone else may not be able to follow my usage of
ITER/LEAVE.  Or, I'll inherit a program using ITER and LEAVE which uses
them improperly.

That's the point of having things like standards and structured
programming-- not to make a set of rules to which everyone may adhere to
blindly, but to make it generally easier for you to develop your own code
and for someone else to fix that code.

If ITER/LEAVE can be used properly, by all means, do so... just think
twice-- some other poor clod out there may not be able to follow your
logic, and may have a terrible time with your code.  The most embarassing
part is when that poor clod happens to be yourself, six months down the
road.

Look after yerselves...

-Doc



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