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JaniczekJaniczek
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Add List.Extra.takeRight and dropRight (#90)
* Add List.Extra.takeRight and dropRight * Split takeWhileRight and dropWhileRight test groups * Add benchmarks
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‎benchmarks/src/Benchmarks.elm‎

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@@ -18,9 +18,11 @@ import Benchmark exposing (Benchmark, describe)
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import Benchmark.Alternative exposing (rank)
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import Benchmark.Runner.Alternative as BenchmarkRunner
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import List.Extra
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import List.Extra.DropRight
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import List.Extra.GroupsOf
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import List.Extra.Lift
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import List.Extra.NotMember
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import List.Extra.TakeRight
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import List.Extra.Unfoldr
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import List.Extra.UniquePairs
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import Maybe.Extra.AndMap
@@ -192,6 +194,9 @@ listExtra =
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intList =
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List.range 1 100
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longList =
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List.range 1 1000
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in
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describe "List.Extra"
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([ rank "uniquePairs"
@@ -234,6 +239,42 @@ listExtra =
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[ ( "Original", List.Extra.NotMember.notMemberOriginal )
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, ( "Simplified", List.Extra.NotMember.notMemberSimple )
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]
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, rank "dropRight 5 10"
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(\dropRight -> dropRight 5 shortList)
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[ ( "foldr", List.Extra.DropRight.dropRightFoldr )
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, ( "reverse", List.Extra.DropRight.dropRightReverse )
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, ( "length", List.Extra.DropRight.dropRightLength )
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]
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, rank "takeRight 5 10"
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(\takeRight -> takeRight 5 shortList)
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[ ( "foldr", List.Extra.TakeRight.takeRightFoldr )
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, ( "reverse", List.Extra.TakeRight.takeRightReverse )
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, ( "length", List.Extra.TakeRight.takeRightLength )
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]
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, rank "dropRight 50 100"
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(\dropRight -> dropRight 50 intList)
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[ ( "foldr", List.Extra.DropRight.dropRightFoldr )
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, ( "reverse", List.Extra.DropRight.dropRightReverse )
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, ( "length", List.Extra.DropRight.dropRightLength )
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]
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, rank "takeRight 50 100"
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(\takeRight -> takeRight 50 intList)
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[ ( "foldr", List.Extra.TakeRight.takeRightFoldr )
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, ( "reverse", List.Extra.TakeRight.takeRightReverse )
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, ( "length", List.Extra.TakeRight.takeRightLength )
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]
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, rank "dropRight 500 1000"
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(\dropRight -> dropRight 500 longList)
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[ ( "foldr", List.Extra.DropRight.dropRightFoldr )
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, ( "reverse", List.Extra.DropRight.dropRightReverse )
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, ( "length", List.Extra.DropRight.dropRightLength )
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]
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, rank "takeRight 500 1000"
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(\takeRight -> takeRight 500 longList)
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[ ( "foldr", List.Extra.TakeRight.takeRightFoldr )
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, ( "reverse", List.Extra.TakeRight.takeRightReverse )
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, ( "length", List.Extra.TakeRight.takeRightLength )
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]
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]
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++ List.concatMap toComparisonsGroupsOfWithStep (List.range 1 4)
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)

‎benchmarks/src/List/Extra/DropRight.elm‎

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@@ -0,0 +1,32 @@
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module List.Extra.DropRight exposing
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( dropRightFoldr
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, dropRightLength
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, dropRightReverse
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)
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dropRightFoldr : Int -> List a -> List a
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dropRightFoldr n lst =
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let
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step x ( n_, acc ) =
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if n_ > 0 then
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( n_ - 1, acc )
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else
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( 0, x :: acc )
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in
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List.foldr step ( n, [] ) lst
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|> Tuple.second
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dropRightReverse : Int -> List a -> List a
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dropRightReverse n lst =
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lst
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|> List.reverse
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|> List.drop n
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|> List.reverse
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dropRightLength : Int -> List a -> List a
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dropRightLength n lst =
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lst |> List.take (List.length lst - n)

‎benchmarks/src/List/Extra/TakeRight.elm‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,33 @@
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module List.Extra.TakeRight exposing
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( takeRightFoldr
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, takeRightLength
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, takeRightReverse
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)
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takeRightFoldr : Int -> List a -> List a
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takeRightFoldr n lst =
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let
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step x ( n_, acc ) =
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if n_ > 0 then
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( n_ - 1, x :: acc )
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else
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-- Wish we could stop here. List.Extra.stoppableFoldr where are you?
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( 0, acc )
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in
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List.foldr step ( n, [] ) lst
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|> Tuple.second
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takeRightReverse : Int -> List a -> List a
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takeRightReverse n lst =
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lst
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|> List.reverse
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|> List.take n
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|> List.reverse
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takeRightLength : Int -> List a -> List a
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takeRightLength n lst =
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lst |> List.drop (List.length lst - n)

‎src/List/Extra.elm‎

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Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@ module List.Extra exposing
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, intercalate, transpose, subsequences, permutations, interweave, cartesianProduct, uniquePairs
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, foldl1, foldr1, indexedFoldl, indexedFoldr, Step(..), stoppableFoldl
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, scanl, scanl1, scanr, scanr1, mapAccuml, mapAccumr, unfoldr, iterate, initialize, cycle, reverseRange
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, splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, conditional, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
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, splitAt, splitWhen, takeRight, dropRight, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, conditional, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
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, isPrefixOf, isSuffixOf, isInfixOf, isSubsequenceOf, isPermutationOf
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, notMember, find, elemIndex, elemIndices, findIndex, findIndices, findMap, count
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, zip, zip3
@@ -37,7 +37,7 @@ module List.Extra exposing
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# Sublists
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@docs splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, conditional, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
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@docs splitAt, splitWhen, takeRight, dropRight, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, conditional, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
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# Predicates
@@ -1592,6 +1592,32 @@ splitWhen predicate list =
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|> Maybe.map (\i -> splitAt i list)
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{-| Take the last _n_ members of a list.
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take 2 [ 1, 2, 3, 4, 5 ] == [ 1, 2 ]
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-}
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takeRight : Int -> List a -> List a
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takeRight n lst =
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lst
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|> List.reverse
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|> List.take n
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|> List.reverse
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{-| Drop the last _n_ members of a list.
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dropRight 2 [ 1, 2, 3, 4, 5 ] == [ 1, 2, 3 ]
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-}
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dropRight : Int -> List a -> List a
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dropRight n lst =
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lst
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|> List.reverse
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|> List.drop n
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|> List.reverse
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{-| Take elements from the right, while predicate still holds.
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takeWhileRight ((<) 5) (List.range 1 10)

‎tests/ListTests.elm‎

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Original file line numberDiff line numberDiff line change
@@ -468,11 +468,77 @@ all =
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\() ->
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Expect.equal (List.Extra.splitWhen (\n -> n == 6) [ 1, 2, 3, 4, 5 ]) Nothing
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]
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, describe "takeRight" <|
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[ test "keeps the correct items" <|
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\() ->
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List.Extra.takeRight 3 (List.range 1 5)
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|> Expect.equal [ 3, 4, 5 ]
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, fuzz2 (Fuzz.int |> Fuzz.map (\n -> -(abs n))) (Fuzz.list Fuzz.int) "non-positive number of items" <|
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\negativeN list ->
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List.Extra.takeRight negativeN list
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|> Expect.equalLists []
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, fuzz2 (Fuzz.intRange 0 10) (Fuzz.list Fuzz.int) "taking more than there is" <|
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\add list ->
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List.Extra.takeRight (List.length list + add) list
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|> Expect.equalLists list
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, fuzz (Fuzz.listOfLengthBetween 1 5 Fuzz.int) "taking last item" <|
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\list ->
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case List.Extra.last list of
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Nothing ->
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Debug.todo "fuzzer bug?"
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Just last ->
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List.Extra.takeRight 1 list
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|> Expect.equalLists [ last ]
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, fuzz (Fuzz.listOfLengthBetween 1 5 Fuzz.int) "taking all but first item" <|
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\list ->
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case List.tail list of
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Nothing ->
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Debug.todo "fuzzer bug?"
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Just butFirst ->
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List.Extra.takeRight (List.length list - 1) list
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|> Expect.equalLists butFirst
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]
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, describe "dropRight" <|
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[ test "drops the correct items" <|
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\() ->
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List.Extra.dropRight 3 (List.range 1 5)
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|> Expect.equal [ 1, 2 ]
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, fuzz2 (Fuzz.int |> Fuzz.map (\n -> -(abs n))) (Fuzz.list Fuzz.int) "non-positive number of items" <|
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\negativeN list ->
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List.Extra.dropRight negativeN list
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|> Expect.equalLists list
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, fuzz2 (Fuzz.intRange 0 10) (Fuzz.list Fuzz.int) "dropping more than there is" <|
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\add list ->
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List.Extra.dropRight (List.length list + add) list
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|> Expect.equalLists []
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, fuzz (Fuzz.listOfLengthBetween 1 5 Fuzz.int) "dropping last item" <|
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\list ->
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case List.Extra.init list of
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Nothing ->
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Debug.todo "fuzzer bug?"
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Just init ->
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List.Extra.dropRight 1 list
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|> Expect.equalLists init
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, fuzz (Fuzz.listOfLengthBetween 1 5 Fuzz.int) "dropping all but first item" <|
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\list ->
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case List.head list of
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Nothing ->
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Debug.todo "fuzzer bug?"
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Just first ->
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List.Extra.dropRight (List.length list - 1) list
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|> Expect.equalLists [ first ]
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]
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, describe "takeWhileRight" <|
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[ test "keeps the correct items" <|
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\() ->
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Expect.equal (List.Extra.takeWhileRight (\x -> 5 < x) (List.range 1 10)) [ 6, 7, 8, 9, 10 ]
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, test "drops the correct items" <|
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]
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, describe "dropWhileRight" <|
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[ test "drops the correct items" <|
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\() ->
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Expect.equal (List.Extra.dropWhileRight (\x -> 5 < x) (List.range 1 10)) [ 1, 2, 3, 4, 5 ]
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]

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