From 910ad6db7925b14576d88118420e2a73dd59e1d1 Mon Sep 17 00:00:00 2001
From: salano_ym <53254905+salano-ym@users.noreply.github.com>
Date: Mon, 13 May 2024 09:08:34 +0000
Subject: [PATCH 1/2] =?UTF-8?q?arr.at=E3=82=92=E8=BF=BD=E5=8A=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 CHANGELOG.md                       |  1 +
 docs/primitive-props.md            |  6 +++++
 src/interpreter/primitive-props.ts |  5 ++++
 test/index.ts                      | 40 ++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65815163..6bdc04ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 - `Uri:encode_full`, `Uri:encode_component`, `Uri:decode_full`, `Uri:decode_component`を追加
 - `str.starts_with`,`str.ends_with`を追加
 - `arr.splice`を追加
+- `arr.at`を追加
 
 # 0.18.0
 - `Core:abort`でプログラムを緊急停止できるように
diff --git a/docs/primitive-props.md b/docs/primitive-props.md
index 25b42f01..0045e873 100644
--- a/docs/primitive-props.md
+++ b/docs/primitive-props.md
@@ -128,6 +128,12 @@ _i_ 番目の文字が存在しない場合は null が返されます。
 型: `num`  
 配列の要素数を取得します。
 
+### @(_v_: arr).at(_index_: num, _otherwise_?: value): value
+配列の _index_ の位置の要素を返します。\
+_index_ が負の場合は末尾から数えます。\
+_index_ が範囲外の場合は、代わりに _otherwise_ を返します。\
+_otherwise_ が省略されている場合は`null`になります。
+
 ### @(_v_: arr).push(_i_: value): null
 **【この操作は配列を書き換えます】**  
 配列の最後に要素を追加します。  
diff --git a/src/interpreter/primitive-props.ts b/src/interpreter/primitive-props.ts
index 9c25f7cf..c89a4cb2 100644
--- a/src/interpreter/primitive-props.ts
+++ b/src/interpreter/primitive-props.ts
@@ -414,6 +414,11 @@ const PRIMITIVE_PROPS: {
 
 			return removed[0] ?? NULL;
 		}),
+
+		at: (target: VArr): VFn => FN_NATIVE(async ([index, otherwise], opts) => {
+			assertNumber(index);
+			return target.value.at(index.value) ?? otherwise ?? NULL;
+		}),
 	},
 
 	error: {
diff --git a/test/index.ts b/test/index.ts
index 18e215b9..2e7b993f 100644
--- a/test/index.ts
+++ b/test/index.ts
@@ -3173,6 +3173,46 @@ describe('primitive props', () => {
 				ARR([NUM(1), NUM(4), NUM(5), NUM(6), NUM(7)])
 			]));
 		});
+		
+		test.concurrent('at (without default value)', async () => {
+			const res = await exe(`
+				let arr1 = [10, 20, 30]
+				<: [
+					arr1
+					arr1.at(0), arr1.at(1), arr1.at(2)
+					arr1.at(-3), arr1.at(-2), arr1.at(-1)
+					arr1.at(3), arr1.at(4), arr1.at(5)
+					arr1.at(-6), arr1.at(-5), arr1.at(-4)
+				]
+			`);
+			eq(res, ARR([
+				ARR([NUM(10), NUM(20), NUM(30)]),
+				NUM(10), NUM(20), NUM(30),
+				NUM(10), NUM(20), NUM(30),
+				NULL, NULL, NULL,
+				NULL, NULL, NULL,
+			]));
+		});
+		
+		test.concurrent('at (with default value)', async () => {
+			const res = await exe(`
+				let arr1 = [10, 20, 30]
+				<: [
+					arr1
+					arr1.at(0, 100), arr1.at(1, 100), arr1.at(2, 100)
+					arr1.at(-3, 100), arr1.at(-2, 100), arr1.at(-1, 100)
+					arr1.at(3, 100), arr1.at(4, 100), arr1.at(5, 100)
+					arr1.at(-6, 100), arr1.at(-5, 100), arr1.at(-4, 100)
+				]
+			`);
+			eq(res, ARR([
+				ARR([NUM(10), NUM(20), NUM(30)]),
+				NUM(10), NUM(20), NUM(30),
+				NUM(10), NUM(20), NUM(30),
+				NUM(100), NUM(100), NUM(100),
+				NUM(100), NUM(100), NUM(100),
+			]));
+		});
 	});
 });
 

From 3c164d9aded81a5feb725b828c886810ff77d336 Mon Sep 17 00:00:00 2001
From: salano_ym <53254905+salano-ym@users.noreply.github.com>
Date: Fri, 17 May 2024 13:37:41 +0000
Subject: [PATCH 2/2] changelog

---
 unreleased/arr-at.md | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 unreleased/arr-at.md

diff --git a/unreleased/arr-at.md b/unreleased/arr-at.md
new file mode 100644
index 00000000..ce3a746f
--- /dev/null
+++ b/unreleased/arr-at.md
@@ -0,0 +1 @@
+- `arr.at`を追加