Unverified Commit 87c5a6a8 authored by Silvan Mosberger's avatar Silvan Mosberger Committed by GitHub
Browse files

Merge pull request #243511 from tweag/lib.lists.hasPrefix 

`lib.lists.{hasPrefix,removePrefix}`: init
parents 50d11650 9fdc0bb2

lib/lists.nix

+34 −0
Original line number Diff line number Diff line
@@ -638,6 +638,40 @@ 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;



  /* 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

+38 −0
Original line number Diff line number Diff line
@@ -492,6 +492,44 @@ 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;

  };



  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; }