Inverting a binary tree (Haskell)

bintree.hs

module BinTrees where

data BinTree a =
  Node a (BinTree a) (BinTree a)
  | Nil
  deriving (Show, Eq)

leaf :: a -> BinTree a
leaf a = Node a Nil Nil

inverse :: BinTree a -> BinTree a
inverse Nil = Nil
inverse (Node a l r) = Node a (inverse r) (inverse l)

{-
$ stack ghci

Warning: No local targets specified, so ghci will not use any options from your package.yaml / *.cabal files.
         
         Potential ways to resolve this:
         * If you want to use the package.yaml / *.cabal package in the current directory, use stack init to create a
           new stack.yaml.
         * Add to the 'packages' field of /Users/milad.bourhani/.stack/global-project/stack.yaml
         
Configuring GHCi with the following packages: 
GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /private/var/folders/py/ps94yrz97g996d0qtnbsjtbcvtv54l/T/ghci41025/ghci-script
Prelude> :l bintree.hs
[1 of 1] Compiling BinTrees         ( bintree.hs, interpreted )
Ok, modules loaded: BinTrees.
*BinTrees> tree = Node 1 ( Node 2 (leaf 4) (leaf 5) ) ( Node 3 (leaf 6) (leaf 7) )
*BinTrees> inverse tree
Node 1 (Node 3 (Node 7 Nil Nil) (Node 6 Nil Nil)) (Node 2 (Node 5 Nil Nil) (Node 4 Nil Nil))
*BinTrees> 
Leaving GHCi.
-}