[darcs-users] darcs conflicts/dependencies -- is patch theory the place to start?

[AntC]

AntC <anthony_clayden <at> clear.net.nz> writes:

> 
> Owen Stephens <darcs <at> owenstephens.co.uk> writes:
> 
> > The complications arise due to the need to be able to conceptually 
consider a
> > darcs repo as a *set* of patches, where the order in which (non-dependent)
> > patches are pulled doesn't matter.
> 
>  yes I understand a repo is conceptually a *set* of patches, and not a 
> DAG [as KevinQ points out]. And yet ... by the time you've commuted a patch 
> round to the target of a pull, it might have morphed quite a bit. It has the 
> same 'moral effect' but is it the *same* patch??
> 

This is how I think of the sameness of patches, but is it too much of a fairy 
story? ...

Each primitive patch has:
- an action -- create/delete/modify/move
- a target or location -- directory for a file action, line num for a hunk
                       -- a move has two locations, source and target
- a content -- file name to create, text to remove/insert (so two contents)
            -- a move has null content

Inverting a primitive patch does one of:
- either 'flips' the action -- create 'flips' to delete, etc
- Xor 'flips' the locations -- as with inverting a move
- Xor 'flips' the content -- flips text to insert/remove

Commuting two primitive patches (providing they don't conflict):
- keeps the same action for each
- possibly adjusts the location
- keeps the same content(s)

Does that thinking help understanding? Or does it confuse more?


Perhaps a file copy can't be fitted in to this model? So perhaps a copy should 
be seen as non-primitive? I see that inverting and commuting file copies is 
problematic(?)


[The Swierstra et al paper has even more primitive actions: a modify is a 
combination of primitive delete + primitive insert; a file rename/move is a 
delete + create -- but note that the file content is held elsewhere under the 
file's id.]


AntC