restructure diff3 a bit

src/Diff3.hs

@@ -1,15 +1,28 @@
 {-# LANGUAGE TupleSections #-}
 
-module Diff3 where
+module Diff3
+  ( diff3Toks
+  ) where
 
 import Diff
 import Merge
 import Types
 
-diff3Toks :: MergeOpts -> TV -> TV -> TV -> Diff
-diff3Toks mo tMine tOrig tYour =
-  conflict $ align (diffToks tOrig tMine) (diffToks tOrig tYour)
+stable :: (Origin, a) -> Bool
+stable (Stable, _) = True
+stable _ = False
+
+applySplit :: (a -> Bool) -> ([a] -> [b]) -> ([a] -> [b]) -> [a] -> [b]
+applySplit cond f g xs = f (takeWhile cond xs) ++ g (dropWhile cond xs)
+
+conflict :: MergeOpts -> [(Origin, (Op, Tok))] -> [(Op, Tok)]
+conflict mo = go
   where
+    go [] = []
+    go as@(a:_)
+      | stable a = applySplit stable (map snd) go as
+      | otherwise = applySplit (not . stable) (merge mo) go as
+
 align :: Diff -> Diff -> [(Origin, (Op, Tok))]
 align ((Keep, a):as) ((Keep, _):bs) = (Stable, (Keep, a)) : align as bs
 align ((Add, a):as) ((Add, b):bs) =
@@ -28,12 +41,7 @@ diff3Toks mo tMine tOrig tYour =
 align as@((Add, _):_) [] = map (Mine, ) as
 align [] bs@((Add, _):_) = map (Your, ) bs
 align _ _ = error "Internal failure: diffstreams seem broken, cannot align"
-    conflict :: [(Origin, (Op, Tok))] -> Diff
-    conflict [] = []
-    conflict as@(a:_)
-      | stable a = applySplit stable (map snd) conflict as
-      | otherwise = applySplit (not . stable) (merge mo) conflict as
-    applySplit :: (a -> Bool) -> ([a] -> [b]) -> ([a] -> [b]) -> [a] -> [b]
-    applySplit cond f g xs = f (takeWhile cond xs) ++ g (dropWhile cond xs)
-    stable (Stable, _) = True
-    stable _ = False
+
+diff3Toks :: MergeOpts -> TV -> TV -> TV -> Diff
+diff3Toks mo tMine tOrig tYour =
+  conflict mo $ align (diffToks tOrig tMine) (diffToks tOrig tYour)