parse error (possibly incorrect indentation or mismatched brackets) error

Question

I've been trying to get my program to work but I always get the same error. enter image description here

And this is my code

type Nat0                = Int
type Zeichenreihe        = String
type Teilzeichenreihe    = String
type IstTeilzeichenreihe = Bool
type Zerlegungszeuge     = (Zeichenreihe,Zeichenreihe,Zeichenreihe)
type Zerlegungszeugen    = [Zerlegungszeuge]


-- Aufgabe A.1

ist_tzr :: Zeichenreihe -> Teilzeichenreihe -> IstTeilzeichenreihe


ist_tzr _ [] = True
ist_tzr [] _ = False
ist_tzr (x:xs) (y:ys)
 | x == y = ist_tzr xs ys
 | otherwise ist_tzr xs (y:ys) 

Answer 1

You're missing a = sign on the very last line:

 | otherwise ist_tzr xs (y:ys) 

It should be:

 | otherwise = ist_tzr xs (y:ys)