Eric Kow wrote:
Heinrich Apfelmus wrote:
In any case, I once again would like to stress that it is my
belief that
commutation is already too complicated to be a suitable foundation
for
understanding the semantics of merges.
In other words, thinking about the intricacies of commutation is a
waste
of our precious brain cycles. :) They are better spent on a simpler
formalization where each line has its own GUID.
So, one of things I thought was attractive about Darcs patch theory is
that it seems to be completely independent of the patch types.
You define patch types, inverse and commutation and the theory takes
care of the rest (cherry picking, merging, conflicts).
Well, patch theory would take care of the rest if it were as mature
as we'd like to. :-) What I'm saying is that, in my opinion, GUIDs
make building a mature theory much easier because they eliminate
commutation altogether.
(My litmus test for maturity of a theory is that I can read it up
somewhere and implement my own toy darcs, just like I can implement
my own toy lambda calculus or my own toy type inference, for example.)
Being agnostic of patch types sounds great, but neither do I expect
GUIDs to be less agnostic, nor is Darcs patch theory as agnostic as
it may sound. The thing is that the commutation operation has to obey
a lot of rules ("patch laws"), some of which are collected in Judah's
paper and some of which are hitherto unknown, and if you introduce a
new patch type, it might just not be possible to make it obey the
patch laws.
Right now the kinds of primitive patch Darcs knows about:
- hunks (the most obvious)
- add A, remove A, adddir D, rmdir D (book-keeping, perhaps)
- move A B
The "Principled Approach to Version Control"[1] shows that GUIDs can
do these.
[1]: http://www.cse.chalmers.se/~wouter/Publications/
PrincipledVersionControl.pdf
- replace tok1 tok2 (not everybody likes this)
Not sure about this one, but I think some weaker form can be done
with GUIDs as well, for example by lexing the whole file and giving
every token a unique GUID.
Some things people have asked for:
- char hunks
Every char gets its own GUID...
- hunk movement
- some kind of tree structure editing
What are these? But yes, there might be patch types that cannot be
formulated in terms of GUIDs. (Not sure whether this is a problem,
though.)
Regards,
apfelmus
--
http://apfelmus.nfshost.com
_______________________________________________
darcs-users mailing list
[email protected]
http://lists.osuosl.org/mailman/listinfo/darcs-users
