Add code for TemplateMethod example

README.md

@@ -586,14 +586,16 @@ newtype WallTime = WallTime (Int, Int) deriving (Show)
 
 -- this is our backend. It can add minutes to a WallTime representation
 addMinutesToWallTime :: Int -> WallTime -> WallTime
-addMinutesToWallTime x (WallTime (h, m)) = 
+addMinutesToWallTime x (WallTime (h, m)) =
     let (hAdd, mAdd) = x `quotRem` 60
         hNew = h + hAdd
-        mNew = m + mAdd        
-    in if mNew >= 60 
-        then WallTime ((hNew + 1) `rem` 24, mNew-60) 
+        mNew = m + mAdd
+    in if mNew >= 60
+        then
+            let (dnew, hnew') = (hNew + 1) `quotRem` 24
+            in  WallTime (24*dnew + hnew', mNew-60)
         else WallTime (hNew, mNew)
-
+        
 -- this is our time representation in Minutes that we want to use in the frontend
 newtype Minute = Minute Int deriving (Show)
 

src/Adapter.hs

@@ -17,12 +17,14 @@ newtype WallTime = WallTime (Int, Int) deriving (Show)
 
 -- this is our backend. It can add minutes to a WallTime representation
 addMinutesToWallTime :: Int -> WallTime -> WallTime
-addMinutesToWallTime x (WallTime (h, m)) = 
+addMinutesToWallTime x (WallTime (h, m)) =
     let (hAdd, mAdd) = x `quotRem` 60
         hNew = h + hAdd
-        mNew = m + mAdd        
-    in if mNew >= 60 
-        then WallTime ((hNew + 1) `rem` 24, mNew-60) 
+        mNew = m + mAdd
+    in if mNew >= 60
+        then
+            let (dnew, hnew') = (hNew + 1) `quotRem` 24
+            in  WallTime (24*dnew + hnew', mNew-60)
         else WallTime (hNew, mNew)
 
 -- this is our time representation in Minutes that we want to use in the frontend

src/Main.hs

@@ -7,6 +7,7 @@ import Composite
 import Visitor
 import Adapter
 import Builder
+import TemplateMethod
 
 main :: IO ()
 main = do
@@ -18,4 +19,5 @@ main = do
   visitorDemo
   adapterDemo
   builderDemo
+  templateMethodDemo
 

src/TemplateMethod.hs

@@ -0,0 +1,34 @@
+module TemplateMethod where
+
+import Adapter (unmarshalWM, marshalMW, addMinutesToWallTime, Minute (..), WallTime (..) )
+
+addMinutesTemplate :: (Int -> WallTime -> WallTime) -> Int -> Minute -> Minute
+addMinutesTemplate tf x =
+    unmarshalWM .
+    tf x .
+    marshalMW
+
+-- implements linear addition even for values > 1440
+linearTimeAdd :: Int -> Minute -> Minute
+linearTimeAdd = addMinutesTemplate addMinutesToWallTime
+
+-- implements cyclic addition, respecting a 24 hour (1440 Min) cycle
+cyclicTimeAdd :: Int -> Minute -> Minute
+cyclicTimeAdd = addMinutesTemplate addMinutesToWallTime'
+
+
+-- a 24 hour (1440 min) cyclic version of addition: 1400 + 100 = 60
+addMinutesToWallTime' :: Int -> WallTime -> WallTime
+addMinutesToWallTime' x (WallTime (h, m)) =
+    let (hAdd, mAdd) = x `quotRem` 60
+        hNew = h + hAdd
+        mNew = m + mAdd
+    in if mNew >= 60
+        then WallTime ((hNew + 1) `rem` 24, mNew-60)
+        else WallTime (hNew, mNew)
+
+templateMethodDemo = do
+    putStrLn "TemplateMethod -> higher order function -> typeclass default implementations"
+    putStrLn $ "linear time: " ++ (show $ linearTimeAdd 100 (Minute 1400))
+    putStrLn $ "cyclic time: " ++ (show $ cyclicTimeAdd 100 (Minute 1400))
+    putStrLn ""