1 files changed, 14 insertions, 7 deletions
diff --git a/src/Mahjong/Tile.hs b/src/Mahjong/Tile.hs
index 05e2f89..b952f48 100644
--- a/src/Mahjong/Tile.hs
+++ b/src/Mahjong/Tile.hs
@@ -1,4 +1,4 @@
-module Tile where
+module Mahjong.Tile where
 
 import Data.Char (toUpper)
 import Data.List (sort)
@@ -32,14 +32,21 @@ is19 c@(MTile col n) = (isCha c) || (isLaoTou c)
 
 orderedTile = sort $ [MTile c n | c<-[Man,Pin,Sou], n <-[1..9]] ++ (map (MTile Cha) [1..7])
 
-nextTile p = if xs /= [] then Just $ head xs
+nextTile' p tiles = if xs /= [] then Just $ head xs
             else Nothing
-    where (x:xs) = dropWhile (/= p) orderedTile
+    where (x:xs) = dropWhile (/= p) tiles
 
-nextTile' :: Maybe MTile -> Maybe MTile
-nextTile' jp = do
-    p <- jp
-    nx@(MTile c n) <- nextTile p
+nextTile :: Maybe MTile -> Maybe MTile
+nextTile jp = do
+    p@(MTile c n) <- jp
     guard ((c /= Cha) && (n /= 9))
+    nx <- nextTile' p orderedTile
     return nx
 
+prevTile jp = do
+    p@(MTile c n) <- jp
+    guard ((c /= Cha) && (n /= 1))
+    nx <- nextTile' p $ reverse orderedTile
+    return nx
+
+