Merge pull request #1298 from pguyot/w39/add-support-for-lists-nthtail

Add support for `lists:nthtail/2`

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

Author: bettio

CHANGELOG.md

@@ -30,6 +30,7 @@ also non string parameters (e.g. `Enum.join([1, 2], ",")`
 - Support for `binary:split/3` and `string:find/2,3`
 - Support for large tuples (more than 255 elements) in external terms.
 - Support for `io:put_chars/2`
+- Support for `lists:nthtail/2`
 
 ### Changed
 

libs/estdlib/src/lists.erl

@@ -32,6 +32,7 @@
 -export([
     map/2,
     nth/2,
+    nthtail/2,
     last/1,
     member/2,
     delete/2,
@@ -92,6 +93,22 @@ nth(1, [H | _T]) ->
 nth(Index, [_H | T]) when Index > 1 ->
     nth(Index - 1, T).
 
+%%-----------------------------------------------------------------------------
+%% @param   N the index to start the sublist from
+%% @param   L the list from which to extract a tail
+%% @returns a sublist of list starting from position N.
+%% @doc     Get the sublist of list L starting after the element N.
+%%
+%%          The behavior of this function is undefined if N is outside of the
+%%          {0..length(L)}.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec nthtail(N :: non_neg_integer(), L :: list()) -> list().
+nthtail(0, L) when is_list(L) ->
+    L;
+nthtail(N, [_H | T]) when is_integer(N) andalso N > 0 ->
+    nthtail(N - 1, T).
+
 %%-----------------------------------------------------------------------------
 %% @param   L the proper list from which to get the last item
 %% @returns the last item of the list.

tests/libs/estdlib/test_lists.erl

@@ -26,6 +26,7 @@
 
 test() ->
     ok = test_nth(),
+    ok = test_nthtail(),
     ok = test_member(),
     ok = test_delete(),
     ok = test_keyfind(),
@@ -57,6 +58,15 @@ test_nth() ->
     ?ASSERT_ERROR(lists:nth(-1, [a, b, c]), function_clause),
     ok.
 
+test_nthtail() ->
+    ?ASSERT_MATCH(lists:nthtail(0, [a, b, c]), [a, b, c]),
+    ?ASSERT_MATCH(lists:nthtail(1, [a, b, c]), [b, c]),
+    ?ASSERT_MATCH(lists:nthtail(2, [a, b, c]), [c]),
+    ?ASSERT_MATCH(lists:nthtail(3, [a, b, c]), []),
+    ?ASSERT_ERROR(lists:nthtail(-1, [a, b, c]), function_clause),
+    ?ASSERT_ERROR(lists:nthtail(4, [a, b, c]), function_clause),
+    ok.
+
 test_member() ->
     ?ASSERT_TRUE(lists:member(a, [a, b, c])),
     ?ASSERT_TRUE(lists:member(b, [a, b, c])),