setR reverses its argument

[LightAndLight]

setR reverses its argument. For example, setR [4, 5, 6] [ 1 * 2 * 3 ] == [ 1 * 2 * 6 5 4 ].

Would you like me to submit a fix?

Attached: a property test suite that helped me diagnose the issue

module Tests.Pivot exposing (pivotTests)

import Expect
import Fuzz exposing (Fuzzer)
import Pivot exposing (Pivot)
import Test exposing (Test, describe)


genPivotInt : Fuzzer (Pivot Int)
genPivotInt =
    Fuzz.map3
        (\a b c -> Pivot.singleton b |> Pivot.setL a |> Pivot.setR c)
        (Fuzz.list Fuzz.int)
        Fuzz.int
        (Fuzz.list Fuzz.int)


genListInt : Fuzzer (List Int)
genListInt =
    Fuzz.list Fuzz.int


pivotTests : Test
pivotTests =
    describe "pivot"
        [ Test.fuzz genPivotInt "setL (getL a) == a" <|
            \pivot ->
                Pivot.setL (Pivot.getL pivot) pivot
                    |> Expect.equal pivot
        , Test.fuzz2 genListInt genPivotInt "getL (setL l a) == l" <|
            \list pivot ->
                Pivot.getL (Pivot.setL list pivot)
                    |> Expect.equal list
        , Test.fuzz genPivotInt "setR (getR a) == a" <|
            \pivot ->
                Pivot.setR (Pivot.getR pivot) pivot
                    |> Expect.equal pivot
        , Test.fuzz2 genListInt genPivotInt "getR (setR l a) == l" <|
            \list pivot ->
                Pivot.getR (Pivot.setR list pivot)
                    |> Expect.equal list
        , Test.fuzz3 Fuzz.int genListInt genPivotInt "goR (setR (x :: xs) a) == Just (setR xs (appendGoR x a))" <|
            \x xs pivot ->
                Pivot.goR (Pivot.setR (x :: xs) pivot)
                    |> Expect.equal (Just (Pivot.setR xs (Pivot.appendGoR x pivot)))

        ]

[yotamDvir]

Yes please!

Certainly getX (setX l a) == l are desired identities, so this is a bug.
Other identities that should hold but are violated relate to appendListR:

• appendListR l (setR [] a) == setR l a
• setR (getR a ++ l) a == appendListR l a

In your submission you are also encouraged to:

1. Add the tests you wrote in a new file tests/Modify.elm in a format similar to the other test files - separate Test for each method, and using tests/Common/Utils.elm.
2. Describe this behavior in the documentation like this.