Commit bc8fbc25 authored by Silvan Mosberger's avatar Silvan Mosberger
Browse files

lib.lists.hasPrefix: init

parent a4f7840e

lib/lists.nix

+15 −0
Original line number Diff line number Diff line
@@ -612,6 +612,21 @@ rec { 
    # Input list

    list: sublist count (length list) list;



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



  Type: hasPrefix :: [a] -> [a] -> bool



  Example:

    hasPrefix [ 1 2 ] [ 1 2 3 4 ]

    => true

    hasPrefix [ 0 1 ] [ 1 2 3 4 ]

    => false

  */

  hasPrefix =

    list1:

    list2:

    take (length list1) list2 == list1;



  /* Return a list consisting of at most `count` elements of `list`,

     starting at index `start`.

lib/tests/misc.nix

+21 −0
Original line number Diff line number Diff line
@@ -480,6 +480,27 @@ runTests { 
    ([ 1 2 3 ] == (take 4 [  1 2 3 ]))

  ];



  testListHasPrefixExample1 = {

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

    expected = true;

  };

  testListHasPrefixExample2 = {

    expr = lists.hasPrefix [ 0 1 ] [ 1 2 3 4 ];

    expected = false;

  };

  testListHasPrefixLazy = {

    expr = lists.hasPrefix [ 1 ] [ 1 (abort "lib.lists.hasPrefix is not lazy") ];

    expected = true;

  };

  testListHasPrefixEmptyPrefix = {

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

    expected = true;

  };

  testListHasPrefixEmptyList = {

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

    expected = false;

  };



  testFoldAttrs = {

    expr = foldAttrs (n: a: [n] ++ a) [] [

    { a = 2; b = 7; }