Commit 782a0e65 authored by Robert Hensing's avatar Robert Hensing
Browse files

lib.dropEnd: init 

Naming borrowed from Haskell
- `base`: [`dropWhileEnd`]
- `extra`, `mono-traversable`, ...: [`dropEnd`]

[`dropEnd`]: https://hackage.haskell.org/package/mono-traversable-1.0.21.0/docs/Data-Sequences.html#v:dropEnd
[`dropWhileEnd`]: https://hackage.haskell.org/package/base-4.21.0.0/docs/Data-List.html#v:dropWhileEnd
parent c96e9078

lib/default.nix

+3 −2
Original line number Diff line number Diff line
@@ -94,8 +94,9 @@ let 
    inherit (self.lists) singleton forEach map foldr fold foldl foldl' imap0 imap1

      filter ifilter0 concatMap flatten remove findSingle findFirst any all count

      optional optionals toList range replicate partition zipListsWith zipLists

      reverseList listDfs toposort sort sortOn naturalSort compareLists take

      drop sublist last init crossLists unique allUnique intersectLists

      reverseList listDfs toposort sort sortOn naturalSort compareLists

      take drop dropEnd sublist last init

      crossLists unique allUnique intersectLists

      subtractLists mutuallyExclusive groupBy groupBy' concatLists genList

      length head tail elem elemAt isList;

    inherit (self.strings) concatStrings concatMapStrings concatImapStrings

lib/lists.nix

+41 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ let 
  inherit (lib.strings) toInt;

  inherit (lib.trivial) compare min id warn pipe;

  inherit (lib.attrsets) mapAttrs;

  inherit (lib) max;

in

rec {
@@ -1484,6 +1485,46 @@ rec { 
    count:

    list: sublist count (length list) list;



  /**

    Remove the last (at most) N elements of a list.





    # Inputs



    `count`



    : Number of elements to drop



    `list`



    : Input list



    # Type



    ```

    dropEnd :: Int -> [a] -> [a]

    ```



    # Examples



    :::{.example}

    ## `lib.lists.dropEnd` usage example



    ```nix

      dropEnd 2 [ "a" "b" "c" "d" ]

      => [ "a" "b" ]

      dropEnd 2 [ ]

      => [ ]

    ```

    :::



   */

  dropEnd =

    n: xs:

      take

        (max 0 (length xs - n))

        xs;



  /**

    Whether the first list is a prefix of the second list.

lib/tests/misc.nix

+12 −0
Original line number Diff line number Diff line
@@ -866,6 +866,18 @@ runTests { 
    (drop 1 [ ] == [ ])

  ];



  testDropEnd = let inherit (lib) dropEnd; in testAllTrue [

    (dropEnd 0 [ 1 2 3 ] == [ 1 2 3 ])

    (dropEnd 1 [ 1 2 3 ] == [ 1 2 ])

    (dropEnd 2 [ 1 2 3 ] == [ 1 ])

    (dropEnd 3 [ 1 2 3 ] == [ ])

    (dropEnd 4 [ 1 2 3 ] == [ ])

    (dropEnd 0 [ ] == [ ])

    (dropEnd 1 [ ] == [ ])

    (dropEnd (-1) [ 1 2 3 ] == [ 1 2 3 ])

    (dropEnd (-1) [ ] == [ ])

  ];



  testListHasPrefixExample1 = {

    expr = lists.hasPrefix [ 1 2 ] [ 1 2 3 4 ];

    expected = true;