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From: bson@rice-chex.ai.mit.edu (Jan Brittenson)
Newsgroups: comp.sys.handhelds
Subject: Re: Forming boolean expressions
Message-ID: <10987@life.ai.mit.edu>
Date: 25 Sep 90 11:13:18 GMT
References: <1990Sep22.163700.15239@mathrt0.math.chalmers.se> <996@halley.UUCP>
Sender: news@ai.mit.edu
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In article <996@halley.UUCP> pedz@halley.UUCP writes:

 > I don't have much insight as to when to use ^MATCH as oppose to
 > VMATCH.  I understand (sorta) how they differ but don't understand
 > when to use one or the other.

Assume you want to make the (very reasonable) reduction of

'&A+(&B+&C)' to '&A+&B+&C'.

With the simple algebraic '1+(2+3)' everything will be just fine,
you'll end up with '1+2+3' either way.

But try it with '1+(2+(3+4))', and you'll end up with 

	vMATCH  ==> '1+2+(3+4)'
	^MATCH  ==> '1+(2+3+4)'

Why is this? Well, ^MATCH looks at the innermost subexpression first
(the bottommost, if you regard the expression as a tree), so the
matching order will be (with the algebraic '1+(2+(3+4))'):


	&A+(&B+&C) vs. '3+4'		(no match)
	  - "" -   vs. '2+(3+4)'	-> '2+3+4'
	  - "" -   vs. '1+(2+3+4)'	(no match)

	==> '1+(2+3+4)'

vMATCH attempts to substitute the topmost level first, so the order
with vMATCH will be:

	&A+(&B+&C) vs. '1+(2+(3+4))'	-> '1+2+(3+4)'
	  - "" -   vs.  '3+4'		(no match)

	==> '1+2+(3+4)'