もういいんじゃないでしょうかね。
ということで、解答です。
私のは、基本的にはku-ma-meさんのと同じですが、18ステップを一発変換に圧縮してます。で、以下の通り。結果的に9分岐になってます。
圧縮の仕方はまた後ほど。こちら。
f :: Tree7 -> Tree f (Leaf, Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) = Leaf f ((Node a Leaf), Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) = (Node a Leaf) f ((Node a (Node b c)), Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) = (Node a (Node b (Node c Leaf))) f (a, (Node b Leaf), Leaf, Leaf, Leaf, Leaf, Leaf) = (Node a (Node b Leaf)) f (a, (Node b (Node c d)), Leaf, Leaf, Leaf, Leaf, Leaf) = (Node a (Node b (Node c (Node d Leaf)))) f (a, b, (Node c d), Leaf, Leaf, Leaf, Leaf) = (Node a (Node b (Node c (Node d (Node Leaf Leaf))))) f (a, b, c, (Node d e), Leaf, Leaf, Leaf) = (Node a (Node b (Node c (Node d (Node e (Node Leaf Leaf)))))) f (a, b, c, d, e, Leaf, Leaf) = (Node a (Node b (Node c (Node d (Node e Leaf))))) f (a, b, c, d, e, f, g) = (Node a (Node b (Node c (Node d (Node e (Node f g)))))) g :: Tree -> Tree7 g Leaf = (Leaf, Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) g (Node a Leaf) = ((Node a Leaf), Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) g (Node a (Node b Leaf)) = (a, (Node b Leaf), Leaf, Leaf, Leaf, Leaf, Leaf) g (Node a (Node b (Node c Leaf))) = ((Node a (Node b c)), Leaf, Leaf, Leaf, Leaf, Leaf, Leaf) g (Node a (Node b (Node c (Node d Leaf)))) = (a, (Node b (Node c d)), Leaf, Leaf, Leaf, Leaf, Leaf) g (Node a (Node b (Node c (Node d (Node Leaf Leaf))))) = (a, b, (Node c d), Leaf, Leaf, Leaf, Leaf) g (Node a (Node b (Node c (Node d (Node e Leaf))))) = (a, b, c, d, e, Leaf, Leaf) g (Node a (Node b (Node c (Node d (Node e (Node Leaf Leaf)))))) = (a, b, c, (Node d e), Leaf, Leaf, Leaf) g (Node a (Node b (Node c (Node d (Node e (Node f g)))))) = (a, b, c, d, e, f, g)
