Re: [Haskell-beginners] Traversing generic trees

Ali, Nested lists with different nesting depths cannot be properly typed. You could probably get around this with a heterogenous collection ( https://wiki.haskell.org/Heterogenous_collections), but the mechanisms proposed there strike me as overkill for this problem. QuasiQuoters could definitely do it, by defining a new grammar construct. That would be quite advanced, and would teach you more about meta-programming than about trees, algorithms or functional programming. Using Imants' suggestion, you would write: n [l 'a', n [l 'b', l 'c', n []], l 'd'] This is just as much boiler plate as you had in your initial definition of tree, but it uses shorter identifiers. Joel On Wed, 22 Jul 2015 19:27 Ali Baharev wrote:

Dear Imants,

Thanks. Unfortunately, I am not sure I get it. It seems to me that it generates a homogeneous list of either nodes with single leaver or just leaves. Or how would the

['a', ['b', 'c', []], 'd']

input look like, when using your proposed approach?

Ali

On Thu, Jul 23, 2015 at 1:10 AM, Imants Cekusins wrote:

...

how about this:

data Tree a = L a | N [Tree a] deriving Show

l::a -> Tree a l = L

n::a -> Tree a n x = N [L x]

m::(a->Tree a) ->[a]-> Tree a m f list = N $ f <$> list

run it like this: m l [2,3] m n [2,3]

any good? _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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