[Haskell-cafe] Re: Newbie request

[Chad Scherrer]

Philip,

you wrote:
-------------------------------------------------------------------------------------
I am trying to learn Haskell. As an exercise, I wrote a
function to create a binary tree in level-order. I am attaching
the code. I am sure there are a number of places where
the code could be improved. Could you please point these out?

Thanks,
Philip

>countNodes :: Tree a -> Integer
>countNodes Empty = 0
>countNodes (Tree rootNode left right) = 1 + countNodes left
                                               + countNodes right
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Stylistically, this is usually written using a fold. Try writing a function

fold :: (a -> b -> b -> b) -> b -> Tree a -> b

Then rewrite countNodes as

countNodes = fold f 0 where f x left right = 1 + left + right

A huge number of other handy functions can then be written in terms of fold.

-- 

Chad Scherrer

"Time flies like an arrow; fruit flies like a banana" -- Groucho Marx
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