Merge pull request #1019 from petermm/lists-split/2

Implement lists:split/2

As implemented in lists: module in OTP
https://github.com/erlang/otp/blob/0e66b88db447954e1de70ec1fa0822d3a7e6133d/lib/stdlib/src/lists.erl#L1808

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

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added support for `pico` and `poci` as an alternative to `mosi` and `miso` for SPI
 - ESP32: Added support to SPI peripherals other than hspi and vspi
 - Added `gpio:set_int/4`, with the 4th parameter being the pid() or registered name of the process to receive interrupt messages
+- Added support for `lists:split/2`
 
 ### Changed
 

libs/estdlib/src/lists.erl

@@ -2,6 +2,7 @@
 % This file is part of AtomVM.
 %
 % Copyright 2017-2023 Fred Dushin <fred@dushin.net>
+% split/2 function Copyright Ericsson AB 1996-2023.
 %
 % Licensed under the Apache License, Version 2.0 (the "License");
 % you may not use this file except in compliance with the License.
@@ -49,6 +50,7 @@
     join/2,
     seq/2, seq/3,
     sort/1, sort/2,
+    split/2,
     usort/1, usort/2,
     duplicate/2,
     sublist/2
@@ -502,6 +504,39 @@ sort(List) when is_list(List) ->
 sort(Fun, List) when is_function(Fun), is_list(List) ->
     quick_sort(Fun, List).
 
+%%-----------------------------------------------------------------------------
+%% @param   N elements non negative Integer
+%% @param   List1 list to split
+%% @returns Tuple with the two lists
+%% @doc     Splits List1 into List2 and List3. List2 contains the first N elements
+%%          and List3 the remaining elements (the Nth tail).
+%% @end
+%%-----------------------------------------------------------------------------
+%% Attribution: https://github.com/erlang/otp/blob/5c8a9cbd125f3db5f5d13ff5ba2a12c076912425/lib/stdlib/src/lists.erl#L1801
+-spec split(N, List1) -> {List2, List3} when
+    N :: non_neg_integer(),
+    List1 :: [T],
+    List2 :: [T],
+    List3 :: [T],
+    T :: term().
+
+split(N, List) when is_integer(N), N >= 0, is_list(List) ->
+    case split(N, List, []) of
+        {_, _} = Result ->
+            Result;
+        Fault when is_atom(Fault) ->
+            erlang:error(Fault, [N, List])
+    end;
+split(N, List) ->
+    erlang:error(badarg, [N, List]).
+
+split(0, L, R) ->
+    {lists:reverse(R, []), L};
+split(N, [H | T], R) ->
+    split(N - 1, T, [H | R]);
+split(_, [], _) ->
+    badarg.
+
 %% Attribution: https://erlang.org/doc/programming_examples/list_comprehensions.html#quick-sort
 %% @private
 quick_sort(Fun, [Pivot | T]) ->

tests/libs/estdlib/test_lists.erl

@@ -41,6 +41,7 @@ test() ->
     ok = test_join(),
     ok = test_seq(),
     ok = test_sort(),
+    ok = test_split(),
     ok = test_usort(),
     ok.
 
@@ -210,6 +211,23 @@ test_sort() ->
 
     ok.
 
+test_split() ->
+    ?ASSERT_MATCH(
+        lists:split(1, ["Foo", "Bar", "Alice", "Bob", "lowercase"]),
+        {["Foo"], ["Bar", "Alice", "Bob", "lowercase"]}
+    ),
+    ?ASSERT_MATCH(
+        lists:split(4, ["Foo", "Bar", "Alice", "Bob", "lowercase"]),
+        {["Foo", "Bar", "Alice", "Bob"], ["lowercase"]}
+    ),
+    ?ASSERT_MATCH(lists:split(0, []), {[], []}),
+    ?ASSERT_MATCH(lists:split(0, ["Foo"]), {[], ["Foo"]}),
+    ?ASSERT_MATCH(lists:split(1, ["Foo"]), {["Foo"], []}),
+    ?ASSERT_ERROR(lists:split(1, []), badarg),
+    ?ASSERT_ERROR(lists:split(2, ["Foo"]), badarg),
+    ?ASSERT_ERROR(lists:split(-1, ["Foo"]), badarg),
+    ok.
+
 test_usort() ->
     ?ASSERT_MATCH(lists:usort([]), []),
     ?ASSERT_MATCH(lists:usort([1]), [1]),