Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!cornell!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.lang.misc
Subject: Structured loops (WAS:Re: Turing programming language.)
Keywords: programming language
Message-ID: <7053@june.cs.washington.edu>
Date: 24 Jan 89 21:56:11 GMT
References: <11@euteal.UUCP> <89Jan20.111000est.4328@turing.toronto.edu> <12@euteal.UUCP>
Reply-To: pardo@cs.washington.edu (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 46

>>[Ongoing discussion of Turing loop structure]

In article <12@euteal.UUCP> mart@euteal.UUCP (Mart van Stiphout) writes:
>[ C's "do", "for", "while" vs. "loop" structring ]
>[What about the following 1.5 loop?]
> while ( i = read() )   { ... code .... }

The above C fragment lets you put only restricted kinds of code inside
the `while' condition (a 1.25 loop?).

There is a more general construct that I've not seen in any existing
programming languages, although (a) doubtless it exists and (b) the
idea is easily a decade old (ok, probably 30, but I *know* at least
10) Substitute your favorite C/Pascal/Lisp/Smalltalk syntax.  In
meta-Algol:

	do ... while boolean ... od;


The conventional "while" loop looks like:

	do while (condition)
	    ...
	od;

The "repeat until" looks like:

	do
	    ...
	while (condition) od;

A single-exit 1.5 loop (most of my 1.5 loops are single exit) looks
like:

	do
	    ...
	while (condition)
	    ...
	od;

The multi-exit 1.5 loop is still less structured.

	;-D on  ( Do ... while ... crazy ... )  Pardo
-- 
		    pardo@cs.washington.edu
    {rutgers,cornell,ucsd,ubc-cs,tektronix}!uw-beaver!june!pardo