Path: utzoo!attcan!uunet!munnari!vuwcomp!windy!srwhmdr
From: srwhmdr@windy.dsir.govt.nz (Malcolm Robbins)
Newsgroups: comp.os.vms
Subject: Bug in VAXTPU searching? (ANY)
Message-ID: <1711@windy.dsir.govt.nz>
Date: 21 Jul 88 14:03:00 GMT
Organization: DSIR, Wellington, NZ
Lines: 90

I've either found a bug in VAXTPU when it does a search for an alphabetic
character at the beginning of a line or, I lack some understanding about
pattern matching.

For example if I construct a TPU procedure to do a search for the following
pattern I find it occaisionally matches an empty line.

	LINE_BEGIN & ANY ('ABCDEFGHIJKLMNOPQRSTUVWXYZ')

In fact, given that a mismatch occurs, the problem can be restricted to
searching for

	LINE_BEGIN & ANY ('G')

say, (assuming that G is what is being matched by accident) and the same
thing occurs.

Furthermore if I cut the area affected and then repaste it in exactly the same
position, so no difference is visible, then the problem disappears!!

If, instead, I remove the ANY and search only for:

	LINE_BEGIN & ANY ('G')

VAXTPU behaves correctly (but this is not what I want to do of course).
Therefore the function ANY appears to be causing the problem.


What I'd like to know is:

  o  Is this problem caused by a lack of understanding on my part or is this
     a VAXTPU bug? Perhaps the mode of the search (Seek versus incremental)
     is causing the unexpected, but "valid" behaviour.

  o  How can I do what I intended, which is to search for an alphabetic
     character at the start of a line, in a reliable way?


For those of you who are raised to the challenge here's a sample TPU procedure
that shows up the problem. Simply compile it and execute it from the top of
a (largish) file with a number of empty lines in it. Hopefully at least one
empty line will match in the unexpected way.

Any replies would be greatly appreciated. In fact to show my appreciation
I'll post a "detab" procedure for removing TABs in a file to this newsgroup
shortly.

------------------------------ Cut Here ------------------------------
PROCEDURE any_bug

LOCAL   pat,
        rng;

pat := LINE_BEGIN &
       ANY ('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz');

LOOP
!
!   Ensure we move off current position for multiple calls to any_bug
!
    MOVE_HORIZONTAL (1);
    rng := SEARCH (pat, FORWARD, EXACT);
    EXITIF rng = 0;
!
!   If the search is successful move to it and see if an empty line has
!   been matched. This should not occur but does.
!
    IF rng <> 0 THEN
	POSITION (rng);
        this_char := CURRENT_CHARACTER;
    	IF this_char = "" THEN
            MESSAGE ('Here is an invalid match!');
	    RETURN;
    	ENDIF;
    ENDIF;
ENDLOOP;

MESSAGE ('No match found');
ENDPROCEDURE
------------------------------ Cut Here ------------------------------


+-----------------------------------------------------------------------------+
| Malcolm Robbins,                                                            |
| Department of Scientific and Industrial Research                            |
| New Zealand.                                                                |
|                                                                             |
| Internet: srwhmdr@wnv.dsir.govt.nz			      		      |
| Pacnet:   PSI%(05301)4600000060::SRWHMDR				      |
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