Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!CITHEX.CALTECH.EDU!carl
From: carl@CITHEX.CALTECH.EDU (Carl J Lydick)
Newsgroups: comp.os.vms
Subject: Re: question on patterns and pattern operators in TPU
Message-ID: <880313023832.53f@CitHex.Caltech.Edu>
Date: 13 Mar 88 10:44:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 24


 > I would like some clarification about patterns and pattern operators in TPU;
 > specifically, the | operator.  If I am interpreting the TPU manual correctly,
 > the line
 > 
 >      PAT := ' ' | LINE_BEGIN;
 > 
 > ought to make a pattern PAT that will match on either a space or a
 > beginning-of-line.  If, however, I follow this line with the lines
 > 
 >      WORDSTART := SEARCH (PAT, REVERSE);
 >      POSITION (WORDSTART);
 > 
 > I always go to a space and never to the beginning of a line, even when
 > the beginning of a line is closer.

You're suffering from one of the wierdnesses of TPU.  Given the pattern
you've specified, TPU will search that part of the file following your current
position for a ' ', and if it doesn't find one, will search it for a LINE_BEGIN.
This is definitely NON-INTUITIVE, and therefore, probably a bad default
(hey DEC, anybody listening out there [though it's far too late to fix this
problem now]).   What you need to do is make the pattern:
	PAT := '' & ( ' ' | LINE_BEGIN ) ;
This forces it to find '' every character and look for ( ' ' | LINE_BEGIN )
as the succeeding character in all cases.