Problem 14

Duplicate each element of a list.

Example

duplicate [1, 2, 3, 5, 8, 8] == [1, 1, 2, 2, 3, 3, 5, 5, 8, 8, 8, 8]

Unit Test

import Html exposing (text)
import List


duplicate : List a -> List a
duplicate list =
    -- your implementation goes here
    []


main =
    text
        (if (test) then
            "Your implementation passed all tests."
         else
            "Your implementation failed at least one test."
        )


test : Bool
test =
    List.all (\(result, expect) -> result == expect)
        [ ( duplicate [1, 2, 3, 5, 8, 8], [1, 1, 2, 2, 3, 3, 5, 5, 8, 8, 8, 8])
        , ( duplicate [], [])
        , ( duplicate [1], [1, 1])
        ]
        && List.all (\(result, expect) -> result == expect)
            [ ( duplicate ["1", "2", "5"], 
                ["1", "1", "2", "2", "5", "5"] )
            ]

Hints

1. Recurse with cons.

Solutions

Solutions