From 9f41d0a432338fc26233512701b0f2f37ce0ab9f Mon Sep 17 00:00:00 2001
From: Rudolph Gottesheim <r.gottesheim@midnight-design.at>
Date: Thu, 21 Dec 2023 16:21:36 +0100
Subject: [PATCH] Add take() function

---
 README.md                     |  1 +
 src/Scope.php                 | 12 ++++++++++++
 tests/unit/ExpressionTest.php |  8 ++++++++
 3 files changed, 21 insertions(+)

diff --git a/README.md b/README.md
index 1578223..d292fc5 100644
--- a/README.md
+++ b/README.md
@@ -106,6 +106,7 @@ The target can be any expression. It will be passed as the first argument to the
 | `contains` | Returns whether a list contains a value                     | `foo:list<string>.contains:bool("bar")`          |
 | `some`     | Returns whether any element matches a [predicate](#lambdas) | `foo:list<int>.some:bool(\|item\| item:int > 5)` |
 | `substr`   | Returns a substring of a string                             | `foo:string.substr:string(0, 5)`                 |
+| `take`     | Returns the first n elements of a list                      | `foo:list<string>.take:list<string>(5)`          |
 
 #### Custom Functions
 
diff --git a/src/Scope.php b/src/Scope.php
index bbe838e..188ccbc 100644
--- a/src/Scope.php
+++ b/src/Scope.php
@@ -11,6 +11,7 @@
 use function array_is_list;
 use function array_keys;
 use function array_map;
+use function array_slice;
 use function array_values;
 use function count;
 use function get_debug_type;
@@ -44,6 +45,7 @@ public function __construct(private readonly array $vars = [], array $funcs = []
             'filter' => self::filter(...),
             'some' => self::some(...),
             'substr' => substr(...),
+            'take' => self::take(...),
         ] : [];
         $shadowed = array_intersect(array_keys($predefinedFuncs), array_keys($funcs));
         if ($shadowed !== []) {
@@ -126,6 +128,16 @@ private static function filter(array $items, callable $predicate): array
         return array_is_list($items) ? array_values($out) : $out;
     }
 
+    /**
+     * @template T
+     * @param list<T> $items
+     * @return list<T>
+     */
+    private static function take(array $items, int $n): array
+    {
+        return array_slice($items, 0, $n);
+    }
+
     /**
      * @internal
      */
diff --git a/tests/unit/ExpressionTest.php b/tests/unit/ExpressionTest.php
index ecaf5fd..6b2760d 100644
--- a/tests/unit/ExpressionTest.php
+++ b/tests/unit/ExpressionTest.php
@@ -126,6 +126,14 @@ public static function evaluateCases(): iterable
                 true,
             ],
             ['myMap:map<int, string>', new Scope(['myMap' => [42 => 'a', 69 => 'b']]), [42 => 'a', 69 => 'b']],
+            [
+                'items:list<string>.take:list<string>(3)',
+                new Scope(['items' => ['a', 'b', 'c', 'd', 'e']]),
+                ['a', 'b', 'c'],
+            ],
+            ['items:list<string>.take:list<string>(3)', new Scope(['items' => ['a', 'b']]), ['a', 'b']],
+            ['items:list<string>.take:list<string>(3)', new Scope(['items' => []]), []],
+            ['items:list<string>.take:list<string>(0)', new Scope(['items' => ['a', 'b', 'c', 'd', 'e']]), []],
         ];
         foreach ($cases as [$expr, $scope, $expected]) {
             $expectedStr = (string)Expr::literal($expected);