Add converge function (#186)

* Add converge function

* Feedback changes

Author: win0err

composer.json

@@ -34,6 +34,7 @@
             "src/Functional/Compose.php",
             "src/Functional/Concat.php",
             "src/Functional/Contains.php",
+            "src/Functional/Converge.php",
             "src/Functional/Curry.php",
             "src/Functional/CurryN.php",
             "src/Functional/Difference.php",

src/Functional/Converge.php

@@ -0,0 +1,46 @@
+<?php
+/**
+ * Copyright (C) 2019 by Sergei Kolesnikov <win0err@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+namespace Functional;
+
+/**
+ * Accepts a converging function and a list of branching functions and returns a new function.
+ *
+ * The results of each branching function are passed as arguments
+ * to the converging function to produce the return value.
+ *
+ * @param callable $convergingFunction Will be invoked with the return values of all branching functions as its arguments
+ * @param callable[] $branchingFunctions A list of functions
+ * @return callable A flipped version of the given function
+ */
+function converge($convergingFunction, array $branchingFunctions)
+{
+    return function (...$values) use ($convergingFunction, $branchingFunctions) {
+        $result = [];
+
+        foreach ($branchingFunctions as $branchingFunction) {
+            $result[] = $branchingFunction(...$values);
+        }
+
+        return $convergingFunction(...$result);
+    };
+}

src/Functional/Functional.php

@@ -49,6 +49,11 @@ final class Functional
      */
     const contains = '\Functional\contains';
 
+    /**
+     * @see \Functional\converge
+     */
+    const converge = '\Functional\converge';
+
     /**
      * @see \Functional\curry
      */

tests/Functional/ConvergeTest.php

@@ -0,0 +1,57 @@
+<?php
+/**
+ * Copyright (C) 2019 by Sergei Kolesnikov <win0err@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+namespace Functional\Tests;
+
+use function Functional\converge;
+
+class ConvergeTest extends AbstractTestCase
+{
+    public function testCallablesAsStrings()
+    {
+        $average = converge('Functional\Tests\div', ['array_sum', 'count']);
+        $this->assertEquals(2.5, $average([1, 2, 3, 4]));
+    }
+
+    public function testCallablesAsAnonymous()
+    {
+        $strangeFunction = converge(
+            function ($u, $l) {
+                return $u . $l;
+            },
+            [
+                'strtoupper',
+                'strtolower',
+            ]
+        );
+
+        $this->assertSame(
+            'FUNCTIONAL PROGRAMMINGfunctional programming',
+            $strangeFunction('Functional Programming')
+        );
+    }
+}
+
+function div($dividend, $divisor)
+{
+    return $dividend / $divisor;
+}