diff options
-rw-r--r-- | lib/lists.nix | 19 | ||||
-rw-r--r-- | lib/tests/misc.nix | 17 |
2 files changed, 36 insertions, 0 deletions
diff --git a/lib/lists.nix b/lib/lists.nix index e12bc9048ef17..c9821819821e7 100644 --- a/lib/lists.nix +++ b/lib/lists.nix @@ -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`. diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix index 5c824a066e16f..4f7035a53f5b4 100644 --- a/lib/tests/misc.nix +++ b/lib/tests/misc.nix @@ -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; } |