Re: view/edit large files

[Ted Zlatanov]

On Fri, 6 Feb 2009 14:20:45 +0100 Mathias Dahl <address@hidden> wrote: 

MD> This is how far I got:
MD> http://www.emacswiki.org/emacs/vlf.el

Thank you, I looked at it and it's almost exactly what I was thinking
originally (but actually implemented :).  I would like it, however, to
be a minor mode rather than a major one so it's more generally useful.
Also writing modifications back is an interesting challenge.

MD> What I do know is that it hits the roof when the file is larger than
MD> that integer limit in Emacs, whatever it is. 

Modifying insert-file-contents to take float or list arguments to
specify the file position should not be too hard--I assume that's the
place where it fails.  Using floats bothers me a bit.  I'd really like
the offet to be a pair of integers, similar to the time storage in
Emacs.

I also got these comments from Chetan Pandya that I wanted to answer
here:
CP> Is this for editing binary files or file with single byte encoding?
CP> If not, it gets more complicated.

It must be single-byte or binary.  insert-file-contents doesn't handle
multibyte encodings and Emacs doesn't have a way to ensure a random seek
is to a valid sequence.  I believe this is all fixable, but I don't know
enough about multibyte encodings to be helpful.

CP> Is this to be the major mode for the file? In that case it may be
CP> OK. Otherwise it wrecks the font lock information and functions that
CP> work with sexp and such syntactic information.

I think as a major mode it's not very useful.  You can use `more' or
`less' from the shell to view a large file in a pager.  hexl-mode would
be a good major mode for large files, for example.

I don't think the font-lock information is very useful for large files
over multiple lines.  The most common case (viewing logs) just needs to
examine a single line.  Can you think of large files that have sexps and
other multiline (over 1000 lines) font-lockable data, which Emacs should
handle?  I can't think of any common ones.  In any case, at worst the
user will fall back to fundamental-mode, and that's better than nothing.

Ted