From mboxrd@z Thu Jan  1 00:00:00 1970
Message-Id: <200311051625.hA5GPmoY019949@localhost.localdomain>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] page as a presentation tool
In-reply-to: <20031105061650.14690.qmail@g.bio.cse.psu.edu>
References: <200311050527.hA55R7nM028163@math.Princeton.EDU> <20031105061650.14690.qmail@g.bio.cse.psu.edu>
From: John Stalker <stalker@Math.Princeton.EDU>
Date: Wed,  5 Nov 2003 11:25:47 -0500
Topicbox-Message-UUID: 7ff4d496-eacc-11e9-9e20-41e7f4b1d025

I should say I am using whatever version is in the ports tree
on FreeBSD.  Maybe there is a better version.  I have noticed
two ways in which it differs.  One is that undo doesn't
restore the dot.  This is pretty annoying since I like to
use succesive refinement to select text and I make a lot of
mistakes.  The other is the 'x' doesn't work quite as
advertised in the paper.  The relevant passage is

	Sam uses a two-pass algorithm for making changes,
	and treats each file as a database against which
	transactions are registered. Changes are not made
	directly to the contents. Instead, when a command
	is started, a `mark' containing a sequence number
	is placed in the transcript Buffer, and each change
	made to the file, either an insertion or deletion or
	a change to the file name, is appended to the end of
	the transcript. When the command is complete, the
	transcript is rewound to the mark and applied to
	the contents.

	One reason for separating evaluation from application
	in this way is to simplify tracking the addresses of
	changes made in the middle of a long sequence. The
	two-pass algorithm also allows all changes to apply
	to the original data: no change can affect another
	change made in the same command. This is particularly
	important when evaluating an x command because it
	prevents regular expression matches from stumbling
	over changes made earlier in the execution.

I haven't looked at the source to see whether UNIX sam also uses
the two pass algorithm, but it is certainly stumbling over changes
made earlier in the execution.

> | sam and the UNIX sam is rather broken.
>
> How so?  It's been ok for me.
>

--
John Stalker
Department of Mathematics
Princeton University
(609)258-6469