Show instance generates invalid Haskell code

Most datatypes implement `Show` in such a way that the result is a valid Haskell code (maybe with some extensions turned on, but still). However, before fixing the `Show` instance, I would consider a better way to encode `Book`s. E.g. something like this (although I'm not sure if it's possible):

```
Book [#age =: 30, #name =: "Jane"]
```
