Problem 7
(**) Flatten a nested list structure.
Transform a list, possibly holding lists as elements into a `flat’ list by replacing each list with its elements (recursively).
Example:
* (my-flatten '(a (b (c d) e))) (A B C D E)
Example in Haskell:
We have to define a new data type, because lists in Haskell are homogeneous.
data NestedList a = Elem a | List [NestedList a]
*Main> flatten (Elem 5) [5] *Main> flatten (List [Elem 1, List [Elem 2, List [Elem 3, Elem 4], Elem 5]]) [1,2,3,4,5] *Main> flatten (List []) []
Solution:
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| data NestedList a = Elem a | List [NestedList a] | |
| deriving Show | |
| flatten :: NestedList a -> [a] | |
| flatten (Elem x) = [x] | |
| flatten (List []) = [] | |
| --flatten (List [Elem x]) = [x] | |
| flatten (List (x:xs)) = flatten x ++ flatten (List xs) | |
| -- let toflat = List [Elem 1, List [Elem 2, List [Elem 3, Elem 4], Elem 5]] | |
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