Elm

Other Elm solutions.

module PhoneNumber exposing (getNumber)


subscriberNumber : Int -> Bool
subscriberNumber n =
    List.member n <| List.range 2 9


parse10Digits : List Int -> Maybe String
parse10Digits digits =
    let
        subscriberN : List Int -> Bool
        subscriberN ns =
            case ns of
                h :: _ ->
                    subscriberNumber h

                [] ->
                    False

        validArea =
            subscriberN digits

        validLocal =
            subscriberN <| List.drop 3 digits

        toStr digitL =
            String.concat <| List.map String.fromInt digitL
    in
    if validArea && validLocal then
        Just <| toStr digits

    else
        Nothing


getNumber : String -> Maybe String
getNumber phoneNumber =
    let
        parseChar c =
            String.toInt <| String.fromList [ c ]

        digits =
            phoneNumber
                |> String.toList
                |> List.filterMap parseChar
    in
    if List.length digits == 11 then
        case digits of
            1 :: remaining ->
                parse10Digits remaining

            _ ->
                Nothing

    else if List.length digits == 10 then
        parse10Digits digits

    else
        Nothing

Roc

Other Roc solutions.

module [clean]

clean : Str -> Result Str _
clean = \phoneNumber ->
    phoneNumber
    |> Str.toUtf8
    |> List.keepIf \c -> c >= '0' && c <= '9'
    |> validateLength
    |> Result.try validateAreaCode
    |> Result.try validateExchangeCode
    |> Result.try Str.fromUtf8

validateAreaCode : List U8 -> Result (List U8) _
validateAreaCode = \phoneNumberBytes ->
    when phoneNumberBytes is
        [head, ..] if head >= '2' && head <= '9' -> Ok phoneNumberBytes
        _ ->
            Err Invalid

validateExchangeCode : List U8 -> Result (List U8) _
validateExchangeCode = \phoneNumberBytes ->
    exchangeCode = List.get phoneNumberBytes 3
    when exchangeCode is
        Ok value if value >= '2' && value <= '9' -> Ok phoneNumberBytes
        _ -> Err Invalid

validateLength : List U8 -> Result (List U8) _
validateLength = \phoneNumberBytes ->
    len = List.len phoneNumberBytes
    if len == 10 then
        Ok phoneNumberBytes
    else if len == 11 then
        when phoneNumberBytes is
            [first, .. as rest] if first == '1' -> Ok rest
            _ -> Err Invalid
    else
        Err Invalid