    -- Copyright (C) 2003 David Roundy
    --
    -- This program is free software; you can redistribute it and/or modify
    -- it under the terms of the GNU General Public License as published by
    -- the Free Software Foundation; either version 2, or (at your option)
    -- any later version.
    --
    -- This program is distributed in the hope that it will be useful,
    -- but WITHOUT ANY WARRANTY; without even the implied warranty of
    -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    -- GNU General Public License for more details.
    --
    -- You should have received a copy of the GNU General Public License
    -- along with this program; see the file COPYING.  If not, write to
    -- the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    -- Boston, MA 02110-1301, USA.

    {-# OPTIONS_GHC -cpp #-}
    {-# LANGUAGE CPP #-}

    #include "gadts.h"

    module Darcs.Patch.Set ( PatchSet, SealedPatchSet ) where

    import Darcs.Hopefully ( PatchInfoAnd )
    import Darcs.Witnesses.Ordered ( RL )
    import Darcs.Witnesses.Sealed ( Sealed )

    -- | A PatchSet is in reverse order, plus has information about which
    -- tags are clean, meaning all patches applied prior to them are in
    -- the tag itself, so we can stop reading at that point.  Just to
    -- clarify, the first patch in a PatchSet is the one most recently
    -- applied to the repo.
    --
    -- 'PatchSet's have the property that if
    -- @
    -- (info $ last $ head a) == (info $ last $ head b)
    -- @
    -- then @(tail a)@ and @(tail b)@ are identical repositories
    --
    -- Questions:
    --
    -- Does this mean that in a patch set such as @[[a b t1 c d e t2][f g
    -- t3] [h i]]@, t1, t2 and t3 are tags, and t2 and t3 are clean?
    --
    -- Can we have PatchSet with length at least 3?
    -- Florent
    type PatchSet p C(x) = RL (RL (PatchInfoAnd p)) C(() x)

    type SealedPatchSet p = Sealed (RL (RL (PatchInfoAnd p)) C(()))