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From: dixon@ihuxa.UUCP
Newsgroups: net.lang.c
Subject: Re: the 'broken' statement
Message-ID: <301@ihuxa.UUCP>
Date: Fri, 7-Oct-83 14:26:06 EDT
Article-I.D.: ihuxa.301
Posted: Fri Oct  7 14:26:06 1983
Date-Received: Sun, 9-Oct-83 08:03:10 EDT
Organization: AT&T Bell Labs, Naperville, Il
Lines: 65

The following article arrived here yesterday:

===============================================================================
>>From ihnp4!clyde!floyd!whuxlb!gummo!harpo!decvax!linus!utzoo!henry Wed Dec 31 18:00:00 1969
>>Relay-Version: version B 2.10.1 7/20/83; site ihuxa.UUCP
>>Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP
>>Path: ihuxa!ihnp4!clyde!floyd!whuxlb!gummo!harpo!decvax!linus!utzoo!henry
>>From: henry@utzoo.UUCP (Henry Spencer)
>>Newsgroups: net.lang.c
>>Subject: the 'broken' statement
>>Message-ID: <3232@utzoo.UUCP>
>>Date: Tue, 4-Oct-83 18:17:02 CDT
>>Article-I.D.: utzoo.3232
>>Posted: Tue Oct  4 18:17:02 1983
>>Date-Received: Thu, 6-Oct-83 01:05:18 CDT
>>References: <322@ucbcad.UUCP>
>>Organization: U of Toronto Zoology
>>Lines: 18
>>
>>Bill Wulf suggested some years ago that in addition to the FOR loop,
>>which is good for operating on all elements of a data structure, there
>>ought to be a FIRST loop for searching data structures:
>>
>>	FIRST i IN something-that-generates-a-sequence-of-values
>>	SUCHTHAT condition
>>	DO
>>		found it
>>	ELSE
>>		not found
>>	END
>>
>>(Ignore the exact punctuation, it was something like that.)  I always
>>thought this was a pretty neat idea.  It's far too late to retrofit
>>it to C, of course.
>>-- 
>>				Henry Spencer @ U of Toronto Zoology
>>				{allegra,ihnp4,linus,decvax}!utzoo!henry
>>
>>
=============================================================================


This proposed construct can be implemented in C as follows:

	for(first-value-in-sequence-of-values; ;advance-to-next-value)
	{
		if(condition)
		{
			found it;
			break;		/*stop loop when first value is found
					 *such that 'condition' is satisfied
					 */
		}
		else
			not found;
	}

This code requires the same number of constructs as that used
in the above article and is reasonably straight forward. So,
the construct 'FIRST i IN' ...  provides only a small marginal
gain over existing C features. Maybe this marginal gain is not
worth the complications it would add to the C compiler.


D A Dixon       ihuxa!dixon      BTL - IH