如何在Haskell中为b->a创建显示实例?

I'm trying to construct a datatype that is essentially a binary tree whose: each node's left branch is a function that can act on the variable in each node's right branch. I'm new to Haskell, and I'm not sure I'm going about this the right way, but my current problem is that I can't figure out how to add my type to the Show typeclass. Here is my attempt: I'm trying to construct a datatype that is esse