From 15c1c43e4b7fe5b3c967caa191521d028970b3fa Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Tue, 13 Jun 2017 21:33:57 -0400
Subject: [PATCH] :fire: Endpoint.

---
 src/SES/Myers.hs | 45 +++++++++++----------------------------------
 1 file changed, 11 insertions(+), 34 deletions(-)

diff --git a/src/SES/Myers.hs b/src/SES/Myers.hs
index b4751a4ec..46b6b90f6 100644
--- a/src/SES/Myers.hs
+++ b/src/SES/Myers.hs
@@ -6,7 +6,6 @@ module SES.Myers
 , EditGraph(..)
 , Distance(..)
 , Diagonal(..)
-, Endpoint(..)
 , ses
 , MyersState
 ) where
@@ -18,7 +17,6 @@ import Data.Functor.Classes
 import Data.These
 import GHC.Show hiding (show)
 import Prologue hiding (for, error)
-import Text.Show (showListWith)
 
 -- | An edit script, i.e. a sequence of changes/copies of elements.
 type EditScript a b = [These a b]
@@ -43,10 +41,6 @@ newtype Distance = Distance { unDistance :: Int }
 newtype Diagonal = Diagonal { unDiagonal :: Int }
   deriving (Eq, Ix, Ord, Show)
 
--- | The endpoint of a path through the edit graph, represented as the x/y indices and the script of edits made to get to that point.
-data Endpoint a b = Endpoint { x :: !Int, script :: !(EditScript a b) }
-  deriving (Eq, Show)
-
 
 -- API
 
@@ -72,12 +66,12 @@ runSES eq (EditGraph as bs)
           where -- | Search an edit graph for the shortest edit script along a specific diagonal, moving onto a given diagonal from one of its in-bounds adjacent diagonals (if any), and sliding down any diagonal edges eagerly.
                 searchAlongK (Diagonal k) = do
                   v <- get
-                  let getK = uncurry Endpoint . (v !) . Diagonal
+                  let getK k = let (x, script) = v ! Diagonal k in (x, x - k, script)
                       prev = getK (pred k)
                       next = getK (succ k)
-                      Endpoint x' script = slideFrom $! if d == 0 || k < negate m || k > n then
+                      (x', _, script) = slideFrom $! if d == 0 || k < negate m || k > n then
                         -- The top-left corner, or otherwise out-of-bounds.
-                        Endpoint 0 []
+                        (0, 0, [])
                       else if k == negate d || k == negate m then
                         -- The lower/left extent of the search region or edit graph, whichever is smaller.
                         moveDownFrom next
@@ -96,19 +90,20 @@ runSES eq (EditGraph as bs)
                   else
                     Nothing
                   where -- | Move downward from a given vertex, inserting the element for the corresponding row.
-                        moveDownFrom (Endpoint x script) = Endpoint x (if (x - pred k) < m then That (bs ! (x - pred k)) : script else script)
+                        moveDownFrom (x, y, script) = (x, succ y, if y < m then That (bs ! y) : script else script)
 
                         -- | Move rightward from a given vertex, deleting the element for the corresponding column.
-                        moveRightFrom (Endpoint x script) = Endpoint (succ x) (if x < n then This (as ! x) : script else script)
+                        moveRightFrom (x, y, script) = (succ x, y, if x < n then This (as ! x) : script else script)
 
                         -- | Slide down any diagonal edges from a given vertex.
-                        slideFrom (Endpoint x script)
+                        slideFrom (x, y, script)
                           | x >= 0, x < n
-                          , (x - k) >= 0, (x - k) < m
+                          , y >= 0, y < m
                           , a <- as ! x
-                          , b <- bs ! (x - k)
-                          , a `eq` b  = slideFrom (Endpoint (succ x) (These a b : script))
-                          | otherwise =            Endpoint       x               script
+                          , b <- bs ! y
+                          , a `eq` b  = slideFrom (succ x,      y, These a b : script)
+                          | otherwise =           (     x, succ y,             script)
+                        x (x, _, _) = x
 
 
 -- Implementation details
@@ -131,26 +126,8 @@ for all run = foldr (\ a b -> (<|>) <$> run a <*> b) (return Nothing) all
 liftShowsVector :: Show i => (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Array.Array i a -> ShowS
 liftShowsVector sp sl d = liftShowsPrec sp sl d . toList
 
--- | Lifted showing of These.
-liftShowsThese :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> These a b -> ShowS
-liftShowsThese sa sb d t = case t of
-  This a -> showsUnaryWith sa "This" d a
-  That b -> showsUnaryWith sb "That" d b
-  These a b -> showsBinaryWith sa sb "These" d a b
-
--- | Lifted showing of edit scripts.
-liftShowsEditScript :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> EditScript a b -> ShowS
-liftShowsEditScript sa sb _ = showListWith (liftShowsThese sa sb 0)
-
--- | Lifted showing of edit graph endpoints.
-liftShowsEndpoint :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> Endpoint a b -> ShowS
-liftShowsEndpoint sp1 sp2 d (Endpoint x script) = showsBinaryWith showsPrec (liftShowsEditScript sp1 sp2) "Endpoint" d x script
-
 
 -- Instances
 
 instance Show2 EditGraph where
   liftShowsPrec2 sp1 sl1 sp2 sl2 d (EditGraph as bs) = showsBinaryWith (liftShowsVector sp1 sl1) (liftShowsVector sp2 sl2) "EditGraph" d as bs
-
-instance Show2 Endpoint where
-  liftShowsPrec2 sp1 _ sp2 _ = liftShowsEndpoint sp1 sp2