I got a little problem which i cannot really solve. I want to map a function over a tree. However, while it compiles it gives out various errors when i want to use it. My idea is that I run "mapTree (+1) someTree" and it adds 1 to every value

My data structure:

```
data BinTree a = Leaf | Branch (BinTree a) a (BinTree a) deriving Show

```

My function: 

```
mapTree func Leaf = func []
mapTree func (Branch left a right) = Branch (mapTree func left) a (mapTree func right)

```

If someone could give me a hint what I am doing wrong...