Path: utzoo!yunexus!oz
From: oz@yunexus.UUCP (Ozan Yigit)
Newsgroups: comp.unix.wizards
Subject: Re: what should egrep '|root' print? (syntax/semantics)
Keywords: regular-expressions
Message-ID: <857@yunexus.UUCP>
Date: 18 Sep 88 00:48:20 GMT
Article-I.D.: yunexus.857
References: <44414@beno.seismo.CSS.GOV> <68203@sun.uucp> <8202@alice.UUCP> <410@quintus.UUCP> <8209@alice.UUCP>
Reply-To: oz@yunexus.UUCP (Ozan Yigit)
Organization: York U. Computing Services - Magic Group
Lines: 31

[Apologies to those getting tired of this topic.]

In article <8209@alice.UUCP> andrew@alice.UUCP (Andrew Hume) writes:
> >it sounds appealing to allow a missing RE to mean the empty string
> but i am unconvinced as to its utility.  
> 

With all due respect, the argument of "utility" except in the
"specific" case of '|foo' (as used by Rick@seismo) is suspect
(bogus?). Unless I am mistaken in the equivalence of (foo)?  and
(foo|E), the issue reduces to one of expression syntax vs semantics.
Is there a good syntactic reason not to allow (foo|) as a valid
expression, such as grammar ambiguity ?? If NOT, I would claim that
the parsers rejecting the expression are "incomplete" (some would
say broken :-), regardless of whether it is in "sam" (Gwyn special,
Argumentum Ad Sam) or wherever.

I agree that "blah(foo||bar)gasp" may not look quite as interesting
(arguably) as "blah(foo|bar)+ptui", but if they are equivalent (yeah,
I know, gasp is not equivalent to ptui. :-) and if there is no solid
syntactic reason to allow one and disallow other, then, why bother
to come up with excuses for it ??

Any thoughts, and/or some real reason against (foo|) ??

oz
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