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From: stevenp@bnr.co.uk (Steven Perryman)
Subject: Re: Software landmines (loops)
Date: 1998/09/03
Message-ID: <6slila$sk1@bmdhh222.bnr.ca>#1/1
X-Deja-AN: 387414154
References: <6sfc2r$6ph$1@hirame.wwa.com> <35eb36d9.729148@news.erols.com>
 <6sfqlr$gat$1@hirame.wwa.com>
Organization: BNR Europe Ltd, London Road, Harlow, England.
Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada
Date: 1998-09-03T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <6sfqlr$gat$1@hirame.wwa.com> "Robert Martin" <rmartin@oma.com> writes:

>The chapter that I have cited and quoted is a general description of
>structured programming, its constituents, its motivations, and its benefits.
>If you are looking for a one-liner, I'm afraid that Dijkstra wasn't
>anticipating you.  But the design heuristic is in the chapter in any case;
>just not conviently isolated into a single quotable sentence.

>The essence of the chapter is that all programs ought to be constructed from
>simpler elements that have singly entry points and single exit points.  The
>motivation is understandabililty and provability.

Correct.

The bottom line has always been this :

Dijkstra defined a set of primitive 'blocks' (if, while etc) .
He asserts some 'state of being' prior to entering each block, and the state
after exiting that block. Using the single-entry single-exit concept, he was
able to precisely reason and verify the behaviour of those blocks. The blocks
can then be used to build higher-level blocks (repeat-until, case etc) .

These concepts then appear to have been taken on by folks like the Yourdon
brigade et al, applied to functions and modules, resulting in the era that
is called 'structured programming' (FWIW, I don't know when the term was
officially first used, as is the case for the term 'OO' ) .

While Elliott rants on looking for the one-liner soundbite that isn't, the
rest of us know and accept that Dijkstra's work very much underpins the
notions of 'structured programming in the small' .


Regards,
Steven Perryman
stevenp@nortel.co.uk