[slime-devel] Re: More steroids for M-. in CMUCL

[Luke Gorrie]

Lynn Quam <quam at ai.sri.com> writes:

> It seems to me that using a good hash code over the entire
> s-expression of the definition would be even better.

The trouble with a hash is that it's very sensitive to modifications
and can be difficult to locate the matching text has moved.

But we can send the whole definition text and then match that if we
like. Currently it sends 256 bytes which I figure will be enough for
most cases.

It would be interesting to have a string matching algorithm that
handles modifications better than incremental-prefix-search, as Alan
suggested.

> It would be useful if the underlying lisp implementation could be
> convinced to include more source location information in the compiled
> object file.  In this way, source version info, such as RCSID, and/or
> file date and time stored in the object file. In the absence of RCSID,
> file date and time could be useful in determining the source file
> version associated with the object file.  Similarly, the sexpr hash
> code could be stored for each definition in object file. 

CMUCL does store the FILE-WRITE-DATE of the source file, so we can
tell if the source has been modified. Currently I use this to cache
the source file if it is known to be unmodified, so that if it is
later edited we still have a good copy. (Even in defun-at-a-time
hacking one often saves the Emacs buffer I think.)

I'm not 100% sure that the cache is worth the bother yet, though. I
will experiment some more.

[About falling back on regexps]
> Unfortunately, using totally different strategies for finding the
> definition source depending on whether the file has changed, is likely
> to lead to confusion for the user, as is often the situation with
> Ilisp.  There are several things that might improve the situation:

I've removed the fallback-on-regexp code now. It could possibly be
useful as an optional feature but for now Helmut has convinced me that
source-paths are good enough.

It did solve the problem I have of finding definitions in CMUCL's CVS
sources while running 18e, but this is a weird thing to be doing in
the first place :-).

Cheers,
Luke