rofrol/Explain Monad using Elm.md

## Explain Monad using Elm.md

      
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              Explain Monad using Elm.md
            
          
    Explain Monad using Elm

Try to guess what will the code display before before clicking Details.
Inspired by https://janiczek.github.io/silent-teacher/.
text

main =
    Html.text "Hello"
Displayed: Hello
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toString

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (Debug.toString maybeHead)
Displayed: Just "one"
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (Debug.toString maybeHead)
Displayed: Nothing
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case

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (case maybeHead of
            Just head ->
                head

            Nothing ->
                ""
        )
Displayed: one
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (case maybeHead of
            Just head ->
                head

            Nothing ->
                ""
        )
Displayed:
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withDefault

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "" maybeHead)
Displayed: one
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "" maybeHead)
Displayed:
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "Empty list" maybeHead)
Displayed: Empty list
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map

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "Empty list" (Maybe.map (\head -> "Head: " ++ head) maybeHead))
Displayed: Head: one
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "Empty list" (Maybe.map (\head -> "Head: " ++ head) maybeHead))
Displayed: Empty list
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list =
    []


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "Empty list" (Maybe.map (\head -> "Head: " ++ head) maybeHead))
Displayed: Empty list
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andThen

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.withDefault "Empty list" (Maybe.andThen (\head -> Just ("Head: " ++ head)) maybeHead))
Displayed: Head: one
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|>

list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (Maybe.map (\head -> "Head: " ++ head) maybeHead |> Maybe.withDefault "Empty list")
Displayed: Head: one
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list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    Html.text
        (maybeHead |> Maybe.map (\head -> "Head: " ++ head) |> Maybe.withDefault "Empty list")
Displayed: Head: one
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list =
    [ "one", "two" ]


maybeHead =
    List.head list


main =
    maybeHead |> Maybe.map (\head -> "Head: " ++ head) |> Maybe.withDefault "Empty list" |> Html.text
Displayed: Head: one
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