Commit 9fdc0bb2 authored by Silvan Mosberger's avatar Silvan Mosberger
Browse files

lib.lists.removePrefix: init

parent bc8fbc25

lib/lists.nix

+19 −0
Original line number Diff line number Diff line
@@ -627,6 +627,25 @@ rec { 
    list2:

    take (length list1) list2 == list1;



  /* Remove the first list as a prefix from the second list.

  Error if the first list isn't a prefix of the second list.



  Type: removePrefix :: [a] -> [a] -> [a]



  Example:

    removePrefix [ 1 2 ] [ 1 2 3 4 ]

    => [ 3 4 ]

    removePrefix [ 0 1 ] [ 1 2 3 4 ]

    => <error>

  */

  removePrefix =

    list1:

    list2:

    if hasPrefix list1 list2 then

      drop (length list1) list2

    else

      throw "lib.lists.removePrefix: First argument is not a list prefix of the second argument";



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

     starting at index `start`.

lib/tests/misc.nix

+17 −0
Original line number Diff line number Diff line
@@ -501,6 +501,23 @@ runTests { 
    expected = false;

  };



  testListRemovePrefixExample1 = {

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

    expected = [ 3 4 ];

  };

  testListRemovePrefixExample2 = {

    expr = (builtins.tryEval (lists.removePrefix [ 0 1 ] [ 1 2 3 4 ])).success;

    expected = false;

  };

  testListRemovePrefixEmptyPrefix = {

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

    expected = [ 1 2 ];

  };

  testListRemovePrefixEmptyList = {

    expr = (builtins.tryEval (lists.removePrefix [ 1 2 ] [ ])).success;

    expected = false;

  };



  testFoldAttrs = {

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

    { a = 2; b = 7; }