Hi, I have brief question about DARCS correctness. I must admit to being more familiar with Operational Transformation theory better than Darcs theory of patches, but I believe the two are very similar. There is a brief intro to OT theory here: http:// revctrl.org/OperationalTransformation . In OT theory there are two correctness constraints on any system, which I believe are related to the two constraints in DARCS that patch commute is its own inverse, and that:
ABC <=> B'A'C <=> B'C'A'' <=> C''B''A'' <=> C''A'''B''' <=> A''''C'''B''' <=> A''''B''''C'''' where A'''' = A, B'''' = B and C'''' = C Basically, if you start off with a set of patches, you may need to transform them to apply them, but if you do it right then the order in which you apply them should not affect the final state of the system. My question is: does that requirement apply to conflicts (merger patches) in the DARCS theory? The reason I ask that question is because my understanding of the DARCS commute operation for textual patches is that it is very similar to Ressel's Transformation Functions in OT theory. These are known NOT to be valid. However, there are no conflicts in OT theory - any result is acceptable as long as you get the same result everywhere. The particular counter example I have for Ressel's transformations, when translated to work with DARCS, causes conflicts. Re-stating the question above in a slightly different form: If I have two Darcs workspaces, each of which have the same set of patches, but in different orders, should these workspaces be identical (even in the presence of conflicts)? If the answer is 'yes', then I have a counter-example. If the answer is 'no', is there a write-up on how this affects correctness? Here is the (possible) counter example (converted to Darcs from the revctrl wiki page mentioned above): #! /bin/sh mkdir darcsTest cd darcsTest mkdir site1 cd site1 darcs init cat > myfile <<EOF Line A Line B Line C EOF darcs add myfile darcs record -am "initial record" --author=EMAIL cd .. darcs get site1 site2 darcs get site1 site3 cd site1 cat > myfile <<EOF Line A Line B Line X Line C EOF darcs record -am "op 1" --author=EMAIL cd ../site2 cat > myfile <<EOF Line A Line C EOF darcs record -am "op 2" --author=EMAIL cd ../site3 cat > myfile <<EOF Line A Line Y Line B Line C EOF darcs record -am "op 3" --author=EMAIL #having set up the operations, lets do some pulls to sync everything #first each of site2 and site3 pulls the other darcs pull -a ../site2 cd ../site2 darcs pull -a ../site3 # next they both pull site1 darcs pull -a ../site1 cd ../site3 darcs pull -a ../site1 # Now we'll check for differences in the result cd .. diff site2/myfile site3/myfile If the final diff outputs anything then the workspaces are in different states after pulling all the patches... and I get output under Darcs 1.0.9rc1 which is the version installed on one of the servers here. Thanks in advance for your thoughts, Will :-} _______________________________________________ darcs-devel mailing list darcs-devel@darcs.net http://lists.osuosl.org/mailman/listinfo/darcs-devel
