[darcs-users] Doubts about commuteFilepatches

Iago Abal iago.abal at gmail.com
Wed Nov 17 16:32:54 UTC 2010


What I can do is to relax the facts I have impose to Hunks in my Alloy model
and check some properties about how commuteHunk works without that
assumptions (for instance, remove my assumption that not empty old or not
empty new).

Question 1: Darcs diff could generate non-sensible hunks? That will be a
bug, I think.

Though thinking about it very quickly....
Let me call Hunk f l [] [] "stupid-hunk": A stupid-hunk h is almost
equivalent to the Identity patch (but it requires h.file to exist, and line
h.line to be in "in bounds"). I think could be easily proved that a
stupid-hunk will always commute with another Hunk. Since modify the line of
a stupid-hunk have no effect, and since -h.new+h.old=-h.old+h.new=0 I think
commuteHunk is well behaved for stupid-Hunks.

(stupid-Hunk should only be offensive for the Hunk!)

On Wed, Nov 17, 2010 at 3:52 PM, Eric Kow <kowey at darcs.net> wrote:

> On Wed, Oct 27, 2010 at 12:40:00 +0100, Iago Abal wrote:
> > commuteFP f (Hunk line1 [] [] :< p2) = seq f $ Succeeded (FP f
> > > (unsafeCoerceP p2) :< FP f (Hunk line1 [] []))
> > >
> > commuteFP f (p2 :< Hunk line1 [] []) = seq f $ Succeeded (FP f (Hunk
> line1
> > > [] []) :< FP f (unsafeCoerceP p2))ç
> > >
> > ...
>
> > Why do you pattern match agains Hunk patches with empty "old" and "new"
> > content? Are they sensible?
>
> Huh.  That looks weird.  I only have more questions :-)
>
> Would you mind looking at commuteHunk and showing what the result would
> be in the 5 cases with and without this commuteFP case?  (In other
> words, falling into the guards [where possible] with one of the hunks
> being empty in this fashion).
>
> It doesn't look like the result would be the same (no line number
> shifting).
>
> Are "empty" hunks like this really supposed to just float past?
> How do they generated?
>
> --
> Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow>
> For a faster response, try +44 (0)1273 64 2905 or
> xmpp:kowey at jabber.fr <xmpp%3Akowey at jabber.fr> (Jabber or Google Talk only)
>
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-- 
Iago Abal Rivas
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