On 06.03.2015 12:13, Julian Foad wrote: > I want to share, briefly, one of the key concepts that is guiding my thinking > about move tracking. It's nothing amazing, in fact it may seem so obvious > that it hardly needs mentioning. What's more surprising is that we haven't > paid more attention to this idea before. > > In order to build a sane merging system, we expect certain symmetries in the > data model. > > Example: > > * start with trunk@9 > commit patch P onto trunk, making trunk@10 > branch trunk@9 to B, making B@11 > merge trunk to B, making B@12 > then: diff(trunk@10, B@12) should be nil > > Bleedin' obvious, heh? > > The idea is that these two things should be symmetrical, interchangeable: > > * a change along a branch > > * a difference between two related branches > > That generalizes to: > > * uniformity of the difference from branch1@r1 to branch2@r2 > for any values of: branch1, r1, branch2, r2 > where branch1 and branch2 are 'related' (formally: in the same branch > family) > > * diffs obey some (more or less obvious) arithmetic rules such as: > diff(A,B) (+) diff(B,C) == diff(A,C) > diff(A,B) (+) diff(B,A) == nil > and so on > > Not just roughly but precisely, testably so.
http://darcs.net/Theory/GaneshPatchAlgebra You've heard of darcs, I take it. :) -- Brane
