module U2Beispiel where


-- Maybe-Typ:

data Maybe' a = Nothing      | Just a
---             (kein Erg.)    (Ergebnis)
                    deriving Show

type Value = Char

lookup' :: Eq a => a -> [ (a,Value) ] -> Maybe' Value
lookup' x []     = Nothing
lookup' x (d:ds) = if x == d1 then Just d2
                             else lookup' x ds
    where (d1,d2) = d
{-
fst :: (a,b) -> a
snd :: (a,b) -> b

ohne Typkontext "Eq a":
 ERROR "U:\PUBLI~$I\cbws03\Uebungen\U2BEI~2_.HS":12 - Cannot justify constraints in explicitly typed binding
*** Expression    : lookup'
*** Type          : a -> [(a,Value)] -> Maybe' Value
*** Given context : ()
*** Constraints   : Eq a        -}

daten :: [(Integer, Value)]
daten = zipWith (,) [ 1 .. 20 ] ['a'..'z']

findChar :: Maybe' Char -> String
findChar Nothing  = "Nix gefunden"
findChar (Just c) = "Gefunden: " ++ [c]