Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!hao!gatech!rayssd!d2b
From: d2b@rayssd.ray.com (Donald A. Borsay)
Newsgroups: comp.os.vms
Subject: Re: FORTRAN Zero Length Strings
Message-ID: <1832@rayssd.ray.com>
Date: 24 Feb 88 17:51:39 GMT
References: <880217133134.2100823c@Iago.Caltech.Edu>
Sender: d2b@rayssd.ray.com (Donald A. Borsay @ Raytheon Company, Portsmouth RI)
Reply-To: d2b@rayssd.RAY.COM (Donald A. Borsay)
Organization: Raytheon Company, Portsmouth RI
Lines: 30
Summary: Double single quote only valid in a quoted string

In article <880217133134.2100823c@Iago.Caltech.Edu> zar@IAGO.CALTECH.EDU (Dan Zirin) writes:
>Another reason you can't type
>	VARIABLE = ''
>is because two single quotes in VAX FORTRAN imply the string "'" (one
>single quote. Even if DEC decided to allow zero length strings, the
>above step would imply an unclosed string or "missing delimiter" error.

Since you use a literal in your example, I'll limit my discussion to
parsing a <literal>.  Currently:

	<literal> = <single-quote> *and* <string> *and* <single-quote>
	<string> = *1_to_many* <character>
	<character> = <non-single-quote> *or* <single-quote> <single-quote>

When allowing zero length strings:

	<literal> = <single-quote> *and* <string> *and* <single-quote>
	<string> = *0_to_many* <character>
	<character> = <non-single-quote> *or* <single-quote> <single-quote>

The key is, the compiler looks ahead one character.  After seeing only
two single quotes in a <literal>, the next character would have to be :

	(1) another single quote (thus continuing the <literal> token),
	(2) whitespace (ending the <literal> token),
     or (3) the beginning of a valid token (ending the <literal> token).

-- 
Don    |Raytheon Company, Submarine Signal Division, Portsmouth, RI
Borsay |ARPAnet: d2b%rayssd.RAY.COM@a.cs.uiuc.edu
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