Vorlesung 2

exampleCode/lecture2/state.hs

@@ -0,0 +1,27 @@
+module Main where
+
+{- Hier eine Passende Definition der State-Monade einfügen...  -}
+{- z.B. Control.Monad.Trans.State aus dem transformers-package -}
+{- oder Control.Monad.State aus dem veralteten mtl-package     -}
+
+type CountState = (Bool, Int)
+ 
+startState :: CountState
+startState = (False, 0)
+
+play :: String -> State CountState Int
+play []     = do
+              (_, score) <- get
+              return score
+play (x:xs) = do
+ (on, score) <- get
+ case x of
+   'C' -> if on then put (on, score + 1) else put (on, score)
+   'A' -> if on then put (on, score - 1) else put (on, score)
+   'T' -> put (False, score)
+   'G' -> put (True, score)
+   _   -> put (on, score)
+ play xs
+
+main = print $ runState (play "GACAACTCGAAT") startState
+-- -> (-3,(False,-3))