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From: barmar@mit-eddie.UUCP (Barry Margolin)
Newsgroups: net.lang
Subject: declarations and nested blocks
Message-ID: <1072@mit-eddie.UUCP>
Date: Mon, 19-Dec-83 02:08:18 EST
Article-I.D.: mit-eddi.1072
Posted: Mon Dec 19 02:08:18 1983
Date-Received: Tue, 20-Dec-83 01:21:10 EST
Organization: MIT, Cambridge, MA
Lines: 31

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There is a feature of PL/I and Algol which is used in most of their
descendents which is both useful and painful.  I am referring to the
fact that the scope of variables includes nested procedures.  It allows
one to write simpler (though less clear) code, but it also permits one
to write incorrect code pretty easily.  This problem is exemplified in
the following fragment:

	do index = 1 to 10;
	     call subr (array (index));
	end;

	subr: procedure (thing);
	      ...
	      do index = 1 to 5;
	      ...
	      end;
	end subr;

Since the programmer forgot to declare a local "index" variable in subr
he ends up with an infinite loop, since index will never reach 10; it
will be set to 5 after each iteration.

I'm surprised that Ada(tm) does not require some explicit statement to
allow you to inherit from an outer block.  Why is this feature
propogated to all new languages, with hardly any change?
-- 
			Barry Margolin
			ARPA: barmar@MIT-Multics
			UUCP: ..!genrad!mit-eddie!barmar