#include "gadts.h"
module Darcs.Patch.Merge
(
Merge(..)
, mergeFL
) where
import Data.Maybe ( fromJust )
import Darcs.Patch.Commute ( Commute )
import Darcs.Witnesses.Ordered ( (:\/:)(..), (:/\:)(..),
FL(..), RL,
reverseFL, reverseRL
)
class Commute p => Merge p where
merge :: (p :\/: p) C(x y)
-> (p :/\: p) C(x y)
instance Merge p => Merge (FL p) where
merge (NilFL :\/: x) = x :/\: NilFL
merge (x :\/: NilFL) = NilFL :/\: x
merge ((x:>:xs) :\/: ys) = fromJust $ do
ys' :/\: x' <- return $ mergeFL (x :\/: ys)
xs' :/\: ys'' <- return $ merge (ys' :\/: xs)
return (ys'' :/\: (x' :>: xs'))
instance Merge p => Merge (RL p) where
merge (x :\/: y) = case merge (reverseRL x :\/: reverseRL y) of
(ry' :/\: rx') -> reverseFL ry' :/\: reverseFL rx'
mergeFL :: Merge p
=> (p :\/: FL p) C(x y)
-> (FL p :/\: p) C(x y)
mergeFL (p :\/: NilFL) = NilFL :/\: p
mergeFL (p :\/: (x :>: xs)) = fromJust $ do
x' :/\: p' <- return $ merge (p :\/: x)
xs' :/\: p'' <- return $ mergeFL (p' :\/: xs)
return ((x' :>: xs') :/\: p'')