Introduce iterable_reduce()

README.md

@@ -72,6 +72,26 @@ foreach (iterable_map($generator(), 'strtoupper') as $item) {
 }
 ```
 
+iterable_reduce()
+--------------
+
+Works like an `reduce` with an `iterable`.
+
+```php
+$generator = function () {
+    yield 1;
+    yield 2;
+};
+
+$reduce = static function ($carry, $item) {
+    return $carry + $item;
+};
+
+var_dump(
+    iterable_reduce($generator(), $reduce, 0))
+); // 3
+```
+
 iterable_filter()
 --------------
 

src/iterable-functions.php

@@ -105,6 +105,33 @@ function iterable_filter($iterable, $filter = null)
 
 }
 
+if (!function_exists('iterable_reduce')) {
+    /**
+     * Reduces an iterable.
+     *
+     * @param iterable<mixed> $iterable
+     * @param callable(mixed, mixed) $reduce
+     * @return mixed
+     *
+     * @psalm-template TValue
+     * @psalm-template TResult
+     *
+     * @psalm-param iterable<TValue> $iterable
+     * @psalm-param callable(TResult|null, TValue) $reduce
+     * @psalm-param TResult|null $initial
+     *
+     * @psalm-return TResult|null
+     */
+    function iterable_reduce($iterable, $reduce, $initial = null)
+    {
+        foreach ($iterable as $item) {
+            $initial = $reduce($initial, $item);
+        }
+
+        return $initial;
+    }
+}
+
 /**
  * @param iterable|array|\Traversable $iterable
  * @param callable|null               $filter

tests/TestIterableReduce.php

@@ -0,0 +1,24 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+
+final class TestIterableReduce extends TestCase
+{
+    public function testArrayReduce()
+    {
+        $iterable = array(1, 2);
+        $reduce = static function ($carry, $item) {
+            return $carry + $item;
+        };
+        self::assertSame(3, iterable_reduce($iterable, $reduce, 0));
+    }
+
+    public function testTraversableReduce()
+    {
+        $iterable = SplFixedArray::fromArray(array(1, 2));
+        $reduce = static function ($carry, $item) {
+            return $carry + $item;
+        };
+        self::assertSame(3, iterable_reduce($iterable, $reduce, 0));
+    }
+}