[Haskell-beginners] Re: about the concatenation on a tree

[Thomas Davie]

>
> hi Bob,
>
> I believe the type of foldTree is implementable, but what confuses  
> me is
>
> the output example:
>
>> concatT (Leaf t) = t
>> concatT (Branch (Leaf t1) (Leaf t2)) = Branch t1 t2
>
> they seem to be inconsistent with the type of concatT which return a  
> Tree only, but in the Leaf case, a atomic value is returned?
>
> anything important I am missing?

You need to remember what type is stored in that Leaf – remember that  
this is a Tree (Tree a) – i.e. the variable t in the line above has  
the type Tree a.

Bob