From 7b622bbcae9d2a1d2d1120e2e308aad1e26c4b8d Mon Sep 17 00:00:00 2001
From: Paul Guyot <pguyot@kallisys.net>
Date: Sun, 22 Sep 2024 16:05:46 +0200
Subject: [PATCH] Add `lists:last/1` and `lists:mapfoldl/3`

Signed-off-by: Paul Guyot <pguyot@kallisys.net>
---
 libs/estdlib/src/lists.erl        | 30 ++++++++++++++++++++++++++++++
 tests/libs/estdlib/test_lists.erl | 15 +++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/libs/estdlib/src/lists.erl b/libs/estdlib/src/lists.erl
index fb9e8ad80c..b6656a729b 100644
--- a/libs/estdlib/src/lists.erl
+++ b/libs/estdlib/src/lists.erl
@@ -32,6 +32,7 @@
 -export([
     map/2,
     nth/2,
+    last/1,
     member/2,
     delete/2,
     reverse/1,
@@ -45,6 +46,7 @@
     keytake/3,
     foldl/3,
     foldr/3,
+    mapfoldl/3,
     all/2,
     any/2,
     flatten/1,
@@ -90,6 +92,16 @@ nth(1, [H | _T]) ->
 nth(Index, [_H | T]) when Index > 1 ->
     nth(Index - 1, T).
 
+%%-----------------------------------------------------------------------------
+%% @param   L the proper list from which to get the last item
+%% @returns the last item of the list.
+%% @doc     Get the last item of a list.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec last(L :: nonempty_list(E)) -> E.
+last([E]) -> E;
+last([_H | T]) -> last(T).
+
 %%-----------------------------------------------------------------------------
 %% @param   E the member to search for
 %% @param   L the list from which to get the value
@@ -372,6 +384,24 @@ foldl(Fun, Acc0, [H | T]) ->
     Acc1 = Fun(H, Acc0),
     foldl(Fun, Acc1, T).
 
+%%-----------------------------------------------------------------------------
+%% @param   Fun the function to apply
+%% @param   Acc0 the initial accumulator
+%% @param   List the list over which to fold
+%% @returns the result of mapping and folding Fun over L
+%% @doc     Combine `map/2` and `foldl/3` in one pass.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec mapfoldl(fun((A, Acc) -> {B, Acc}), Acc, [A]) -> {[B], Acc}.
+mapfoldl(Fun, Acc0, List1) ->
+    mapfoldl0(Fun, {[], Acc0}, List1).
+
+mapfoldl0(_Fun, {List1, Acc0}, []) ->
+    {?MODULE:reverse(List1), Acc0};
+mapfoldl0(Fun, {List1, Acc0}, [H | T]) ->
+    {B, Acc1} = Fun(H, Acc0),
+    mapfoldl0(Fun, {[B | List1], Acc1}, T).
+
 %%-----------------------------------------------------------------------------
 %% @equiv   foldl(Fun, Acc0, reverse(List))
 %% @doc     Fold over a list of terms, from right to left, applying Fun(E, Accum)
diff --git a/tests/libs/estdlib/test_lists.erl b/tests/libs/estdlib/test_lists.erl
index bb7350e65b..133a33f2c0 100644
--- a/tests/libs/estdlib/test_lists.erl
+++ b/tests/libs/estdlib/test_lists.erl
@@ -46,6 +46,8 @@ test() ->
     ok = test_split(),
     ok = test_usort(),
     ok = test_filtermap(),
+    ok = test_last(),
+    ok = test_mapfoldl(),
     ok.
 
 test_nth() ->
@@ -296,4 +298,17 @@ test_filtermap() ->
     ),
     ok.
 
+test_last() ->
+    ?ASSERT_ERROR(lists:last([]), function_clause),
+    ?ASSERT_MATCH(a, lists:last([a])),
+    ?ASSERT_MATCH(b, lists:last([a, b])),
+    ?ASSERT_ERROR(lists:last([a | b]), function_clause),
+    ok.
+
+test_mapfoldl() ->
+    ?ASSERT_MATCH({[], 1}, lists:mapfoldl(fun(X, A) -> {X * A, A + 1} end, 1, [])),
+    ?ASSERT_MATCH({[1, 4, 9], 4}, lists:mapfoldl(fun(X, A) -> {X * A, A + 1} end, 1, [1, 2, 3])),
+    ?ASSERT_ERROR(lists:mapfoldl(fun(X, A) -> {X * A, A + 1} end, 1, foo), function_clause),
+    ok.
+
 id(X) -> X.