Here are various tweaks to patch-related code. Mostly factored out of my 
rebase branch, so some have no obvious immediate value but will help
when merging that later.

Commentary on some of the patches inline:

12 patches for repository darcs-unstable@darcs.net:screened:

Just trying to reduce the dependency on the Patchy class:

Tue May 15 21:52:50 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * drop some unnecessary Patchy constraints


This helps to simplify a type class - it's a method that actually
proved quite problematic when implementing new patch types, and
this is the last in a line of patches to get rid of it:

Wed May 16 07:00:12 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * get rid of joinPatches

Trying to cut down the over-large (IMO) Patchy class:

Wed May 16 08:00:17 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * drop MyEq superclass from Patchy
  The notion of equality on patches isn't completely obvious,
  because it might be structural equality or equality under commutations
  (e.g. for lists of patches).
  So it's better to be explicit about when we need it.
  It moves into PrimPatch instead for now, for V1 and V2 commutation,
  but RealPatch doesn't need it.


This one makes it easier to temporarily drop in debugging code
into generic patch handling code:

Wed May 16 18:36:47 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * add helper class for debugging patches

Making complicated commutes out of simpler commutes, e.g. commuting
lists of patches:

Thu May 17 17:43:18 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * break CommuteFn infrastructure out into separate module

More patch simplification:

Thu May 17 17:55:01 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * drop unnecessary superclasses and move Invert FL/RL instances



Thu May 17 17:55:35 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * add commutation combinators for Named



Thu May 17 18:20:17 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * add utility function for changing type of a ListFormat



Thu May 17 18:35:39 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * add merge combinators

Makes it easier to use resolution code from rebase:

Thu May 31 18:47:36 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * relax type signature


Thu May 31 18:47:58 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * use RepoPatch instead of Patchy constraint for matchers
  This isn't required by the code, but it helps to guard against accidentally
  using the wrong kind of patch.
  

Thu May 31 18:48:28 BST 2012  Ganesh Sittampalam <ganesh@earth.li>
  * make Patchy smaller
  Reading, printing and inspecting the internals are now separate
  which makes it easier to see what functionality is needed where.
  Patchy is left as a core: Apply, Commute and Invert.

Attachments

• drop-some-unnecessary-patchy-constraints.dpatch
• unnamed

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Will accept the bundle, not on the basis that I understand Gasesh'
grand scheme, but that the patches do what they say. (and +1 for the
use of explicit dependencies in the joinPatches patch).

The page http://wiki.darcs.net/Internals/Patches needs more love: it
would be nice to know there what is the purpose of Patchy, RepoPatch,
etc.

g.

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