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99 Elm Problems/Problem 7
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Flatten a nested list structure.
We have to define a new data type, because lists in Elm are homogeneous.
import Html exposing (text)
import List
type NestedList a
= Elem a
| NestedList (List (NestedList a))
flatten : NestedList a -> List a
-- your implementation goes here
main =
text <| toString <|
flatten (NestedList [Elem 1, NestedList [Elem 2, NestedList [Elem 3, Elem 4], Elem 5]])
Result:
[1, 2, 3, 4, 5]
Solutions