solutions block 3

solutions/block3/maybe.hs

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+safeHead :: [a] -> Maybe a
+safeHead [] = Nothing
+safeHead (x:_) = Just x
+
+safeTail :: [a] -> Maybe [a]
+safeTail [] = Nothing
+safeTail (_:xs) = Just xs
+
+safeLast :: [a] -> Maybe a
+safeLast [] = Nothing
+safeLast[x] = Just x
+safeLast (_:xs) = safeLast xs 
+
+safeInit :: [a] -> Maybe [a]
+safeInit [] = Nothing
+safeInit [_] = Just []
+safeInit (x:xs) = fmap ([x] ++) (safeInit xs)

solutions/block3/zauberschule.hs

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+-- 1. Definition der magischen Wesen
+data MagicalCreature = Dragon String Int Int
+                     | Unicorn String Int Int
+                     | Wizard String Int Int
+                    deriving (Show)
+
+-- 2. Beschreibung der magischen Wesen
+describeMagicalCreature :: MagicalCreature -> String
+describeMagicalCreature (Dragon name level experience) = name ++ " ist ein Drache mit Magielevel " ++ show level ++ " und " ++ show experience ++ " Erfahrungspunkten."
+describeMagicalCreature (Unicorn name level experience) = name ++ " ist ein Einhorn mit Magielevel " ++ show level ++ " und " ++ show experience ++ " Erfahrungspunkten."
+describeMagicalCreature (Wizard name level experience) = name ++ " ist ein Zauberer mit Magielevel " ++ show level ++ " und " ++ show experience ++ " Erfahrungspunkten."
+
+-- 3. Kräfte
+class Fighter a where
+  power :: a -> Int
+
+instance Fighter MagicalCreature where
+    power (Dragon _ level experience) = (level + experience) * 3
+    power (Unicorn _ level experience) = (level + experience) * 4
+    power (Wizard _ level experience) = (level + experience) * 5
+
+-- 4. Magisches Duell
+duel :: (Fighter a) => a -> a -> Either String a
+duel fighter1 fighter2
+  | power fighter1 > power fighter2 = Right fighter1
+  | power fighter1 < power fighter2 = Right fighter2
+  | otherwise = Left "Unentschieden!"