Could someone provide an elegant solution to Bird problem 4.2.13?
Here are the problem and my inelegant solution:
Problem
---
Since concatenation seems such a basic operation on lists, we can try to
construct a data type that captures
concatenation as a primitive.
For example,
data (CatL
Mine is somewhat more elegant...
data (CatList a) = CatNil
| Wrap a
| Cat (CatList a) (CatList a) deriving Show
instance (Eq a) => Eq (CatList a) where
CatNil == CatNil = True
Wrap x == Wrap y = x==y
a@(Cat x y) == b
2009/3/4 R J :
> What's the pure solution that uses cases and recursion on
> CatList, not Haskell's built-in lists, to capture the equality of nested
> CatLists?
As Rafael pointed out, the simplest thing to do is to convert to a
canonical form; you can prove that each CatList has a single canonica
Good point Ryan,
I did it in my lunch time and, being in a hurry, overlooked the fact that
left adjust in (*2) is redundant and that (*1) can be completely removed by
using (adjust x). I actually think I added (*2) for "safety"!! :-D
R J, you should take a look on Chris Okasaki's book. This is pr
2009/3/4 R J :
> Could someone provide an elegant solution to Bird problem 4.2.13?
>
> Here are the problem and my inelegant solution:
>
> Problem
> ---
>
> Since concatenation seems such a basic operation on lists, we can try to
> construct a data type that captures
> concatenation as a primit
