[Haskell-cafe] Construct all possible trees

[Mirko Rahn]

I'm afraid, but you are missing a case here. For example the tree

Branch (Leaf 1) (Branch (Leaf 3) (Leaf 2))

is not constructed by your program. Correct is

insert x t@(Leaf y) = [Branch s t, Branch t s]  where s = Leaf x
insert x t@(Branch l r) = [Branch l' r | l' <- insert x l] ++
                           [Branch l r' | r' <- insert x r] ++
        {- missed this: -} [Branch s t,Branch t s] where s = Leaf x

With this modification, your program becomes essentially the same as my 
version but with suboptimal sharing (you construct Leaf x twice and with 
the correction even three times). As a consequence my version is faster 
and eats less memory.

/BR


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