Adds termination to check for matching element in provided collection

src/Reducer/Termination/Has.php

@@ -0,0 +1,47 @@
+<?php
+
+
+namespace Pitchart\Transformer\Reducer\Termination;
+
+
+use Pitchart\Transformer\Reduced;
+use Pitchart\Transformer\Reducer\Traits\HasCallback;
+use Pitchart\Transformer\Termination;
+
+class Has implements Termination
+{
+    /**
+     * @var callable
+     */
+    protected $callback;
+
+    public function __construct(callable $callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function init()
+    {
+        return false;
+    }
+
+    public function step($result, $current)
+    {
+        $callback = $this->callback;
+        if ($callback($current)) {
+            return new Reduced(true);
+        }
+
+        return $result;
+    }
+
+    public function complete($result)
+    {
+        if ($result instanceof Reduced) {
+            return $result->value();
+        }
+
+        return $result;
+    }
+
+}

src/Transducer/transducers.php

@@ -459,8 +459,19 @@ function to_single()
     return new Reducer\Termination\SingleResult();
 }
 
+/**
+ * @param callable $callback
+ *
+ * @return Reducer\Termination\Has
+ */
+function has(callable $callback)
+{
+    return new Reducer\Termination\Has($callback);
+}
+
 /**
  * @param mixed $glue
+ *
  * @return Reducer\Termination\ToString
  */
 function to_string($glue = '')

src/Transformer.php

@@ -341,6 +341,16 @@ public function single()
         return $this->terminate(t\to_single());
     }
 
+    /**
+     * @param callable $callback
+     *
+     * @return mixed
+     */
+    public function has(callable $callback)
+    {
+        return $this->terminate(t\has($callback));
+    }
+
     /**
      * @return mixed
      */

tests/Reducer/Termination/HasTest.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Pitchart\Transformer\Tests\Reducer\Termination;
+
+use Pitchart\Transformer\Reducer;
+use Pitchart\Transformer\Reducer\Termination\Has;
+use PHPUnit\Framework\TestCase;
+use Pitchart\Transformer\Termination;
+use function Pitchart\Transformer\Tests\Fixtures\plus_one;
+use Pitchart\Transformer\Transformer;
+
+class HasTest extends TestCase
+{
+    public function test_is_a_reducer()
+    {
+        $has = new Has(function ($item) { return $item != 0; });
+        self::assertInstanceOf(Reducer::class, $has);
+    }
+
+    public function test_is_a_termination()
+    {
+        $has = new Has(function ($item) { return $item != 0; });
+        self::assertInstanceOf(Termination::class, $has);
+    }
+
+    public function test_returns_true_if_collection_contains_matching_element()
+    {
+        $has = (new Transformer([1, 2, 3, 4]))
+            ->has(function ($item) { return $item != 0; });
+
+        self::assertTrue($has);
+    }
+
+    public function test_returns_false_if_collection_does_not_contain_matching_element()
+    {
+        $has = (new Transformer([1, 2, 3, 4]))
+            ->has(function ($item) { return $item == 0; });
+
+        self::assertFalse($has);
+    }
+
+    /**
+     * @param callable $callback
+     * @param bool $expected
+     *
+     * @dataProvider callableProvider
+     */
+    public function test_applies_after_operation(callable $callback, bool $expected)
+    {
+        $has = (new Transformer([1, 2, 3, 4]))
+            ->map(plus_one())
+            ->has($callback);
+        self::assertEquals($expected, $has);
+    }
+
+    public function callableProvider()
+    {
+        yield from [
+            [function ($item) { return $item == 5; }, true],
+            [function ($item) { return $item == 1; }, false],
+        ];
+    }
+}