What is wrong with my haskell general tree?

Question

Here is my code and there are so many things wrong about it that i can't see. What is the problem? or what "are" the problems?? I get these errors for several lines:

• Data constructor not in scope. NBaum
• Couldn't match expected type [NBaum [Char]]' with actual type `NBaum [Char]'
• In the second argument of NKnoten', namely `(NBlatt "Io")'

• In the sixth argument of `NBaum', namely

  data NBaum a = NBlatt a | NKnoten a [NBaum a]
  deriving(Eq,Show)
  
  
  tree :: NBaum String
  tree  =   
  NBaum "Sonne"  
  (NKnoten "Erde"  
      (NBlatt "MOND"  )
  
  )        
  (NBlatt "Merkur" )  
  (NBlatt "Venus" )  
  
  (NKnoten "MARS" 
  
      (NBlatt "PHOBOS" )  
      (NBlatt "DEIMOS" )  
  )      
  (NKnoten "JUPITER" 
      (NBlatt "Io" )  
      (NBlatt "EUROPA" ) 
      (NBlatt "GANYMED" )
      (NBlatt "KALLISTO" )
  
  ) 
  

Answer 1

The problem is that if you describe a list [], you do this between square brackets separated with commas, like [1,4,2,5]. Not between round brackets: that is a tuple.

tree :: NBaum String
tree  = NKnoten "Sonne" [
    NKnoten "Erde"  [NBlatt "MOND"],
    NBlatt "Merkur",
    NBlatt "Venus",

    NKnoten "MARS" [
        NBlatt "PHOBOS",  
        NBlatt "DEIMOS" 
    ],      
    NKnoten "JUPITER" [
        NBlatt "Io",
        NBlatt "EUROPA",
        NBlatt "GANYMED",
        NBlatt "KALLISTO"
    ]
]

Furthermore - as is highlighted in the code fragment - you (probably accidentally) - wrote the type name (NBaum) instead of constructor name (NKnoten) at the first object (the "Sonne").