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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.pascal
Subject: Re: debug prints (was Re: Linear search again)
Message-ID: <2822@umcp-cs.UUCP>
Date: Fri, 8-Aug-86 21:17:35 EDT
Article-I.D.: umcp-cs.2822
Posted: Fri Aug  8 21:17:35 1986
Date-Received: Sun, 10-Aug-86 20:07:26 EDT
References: <871@minster.UUCP> <2785@umcp-cs.UUCP> <1174@umd5>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 39

>In article <2785@umcp-cs.UUCP> I wrote:
[an example of how a Mesa programmer would probably write `find']:
>>	find: PROC [ch: CHAR, string: LONG STRING]
>>		RETURNS [pos: CARDINAL, found: BOOL];
>>	BEGIN
>>	    FOR i:CARDINAL in [0..String.Length[string]] DO
>>		IF string[i] = ch THEN RETURN [i, TRUE];
>>	    ENDLOOP;
>>	    RETURN [0, FALSE];
>>	END;

In article <1174@umd5> zben@umd5.umd.edu (Ben Cranston) writes:
>I always avoided these nonstandard returns because they make it painful to
>drop in debug print statements.  I would always slap in WRITELN(MYARGS) at
>the top, and WRITELN('Returning from FIND') at the bottom, and wonder why
>I never saw the 'Returning from FIND' output...  If you are trying to find
>an infinite loop this can be really misleading.

Ah, but in Mesa, no one ever seems to use debug prints: for there is
a very complete debugger that is always accessible.  For that matter,
if you did wish to wrap `find' with debug print statements, you could
simply rename the procedure to `findInternal' and add

	-- Again, details may be wrong; all the manuals are four miles
	-- away.
	find: PROC [ch: CHAR, string: LONG STRING]
		RETURNS [pos: CARDINAL, found: BOOL];
	BEGIN
	    Msg.PutMsg["Enter find"L];
	    [pos, found] _ internalFind[ch, string];--`_' represents left-arrow
	    Msg.PutMsg["Exit find"L];
	    RETURN [pos, found];
	END;

Indeed, this technique works in every language.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu