Merge pull request #68 from tPl0ch/feature/listt

Implement `Listt::head` and `Listt::tail`

Author: widmogrod

composer.json

@@ -7,7 +7,8 @@
   "require-dev": {
     "phpunit/phpunit": "^4.7",
     "friendsofphp/php-cs-fixer": "^2",
-    "codeclimate/php-test-reporter": "^0.4.4"
+    "codeclimate/php-test-reporter": "^0.4.4",
+    "giorgiosironi/eris": "^0.9"
   },
   "license": "MIT",
   "authors": [

composer.lock

@@ -580,7 +580,7 @@ function flip(callable $func)
  */
 function isNativeTraversable($value)
 {
-    return is_array($value) || $value instanceof \Traversable;
+    return \is_iterable($value);
 }
 
 /**

src/Functional/functions.php

@@ -16,7 +16,7 @@ class Listt implements
 {
     use Common\PointedTrait;
 
-    const of = 'Widmogrod\Primitive\Listt::of';
+    public const of = 'Widmogrod\Primitive\Listt::of';
 
     /**
      * @param array $value
@@ -35,7 +35,7 @@ public function map(callable $transformation)
     {
         $result = [];
         foreach ($this->value as $value) {
-            $result[] = call_user_func($transformation, $value);
+            $result[] = $transformation($value);
         }
 
         return self::of($result);
@@ -68,11 +68,13 @@ public function bind(callable $transformation)
      */
     public function extract()
     {
-        return array_map(function ($value) {
-            return $value instanceof Common\ValueOfInterface
+        return $this->reduce(function ($accumulator, $value) {
+            $accumulator[] = $value instanceof Common\ValueOfInterface
                 ? $value->extract()
                 : $value;
-        }, $this->value);
+
+            return $accumulator;
+        }, []);
     }
 
     /**
@@ -81,7 +83,7 @@ public function extract()
     public function reduce(callable $function, $accumulator)
     {
         foreach ($this->value as $item) {
-            $accumulator = call_user_func($function, $accumulator, $item);
+            $accumulator = $function($accumulator, $item);
         }
 
         return $accumulator;
@@ -103,7 +105,7 @@ public function traverse(callable $transformation)
 
             return $functor
                 ->map(f\append)
-                ->ap($ys ? $ys : $functor::of([])); // https://github.com/widmogrod/php-functional/issues/30
+                ->ap($ys ?: $functor::of([])); // https://github.com/widmogrod/php-functional/issues/30
         }, false, $this);
     }
 
@@ -125,6 +127,8 @@ public function getEmpty()
 
     /**
      * @inheritdoc
+     *
+     * @throws TypeMismatchError
      */
     public function concat(FantasyLand\Semigroup $value)
     {
@@ -148,4 +152,48 @@ public function equals($other)
             ? $this->extract() === $other->extract()
             : false;
     }
+
+    /**
+     * head :: [a] -> a
+     *
+     * @return mixed First element of Listt
+     *
+     * @throws \BadMethodCallException
+     */
+    public function head()
+    {
+        return $this->guardEmptyGenerator('head of empty Listt')->current();
+    }
+
+    /**
+     * tail :: [a] -> [a]
+     *
+     * @return \Widmogrod\Primitive\Listt
+     *
+     * @throws \BadMethodCallException
+     */
+    public function tail(): self
+    {
+        ($generator = $this->guardEmptyGenerator('tail of empty Listt'))->next();
+
+        return $generator->valid()
+            ? self::of((function ($values) {
+                yield from $values;
+            })($generator))
+            : self::mempty();
+    }
+
+    private function guardEmptyGenerator(string $message): \Generator
+    {
+        /** @var \Generator $generator */
+        $generator = (function ($values) {
+            yield from $values;
+        })($this->value);
+
+        if (!$generator->valid()) {
+            throw new \BadMethodCallException($message);
+        }
+
+        return $generator;
+    }
 }

src/Primitive/Listt.php

@@ -2,6 +2,7 @@
 
 namespace test\Monad;
 
+use Eris\TestTrait;
 use Widmogrod\FantasyLand\Applicative;
 use Widmogrod\FantasyLand\Functor;
 use Widmogrod\FantasyLand\Monoid;
@@ -11,9 +12,13 @@
 use Widmogrod\Helpful\MonadLaws;
 use Widmogrod\Helpful\MonoidLaws;
 use Widmogrod\Primitive\Listt;
+use function Eris\Generator\choose;
+use function Eris\Generator\vector;
 
 class ListtTest extends \PHPUnit_Framework_TestCase
 {
+    use TestTrait;
+
     /**
      * @dataProvider provideData
      */
@@ -149,4 +154,58 @@ public function provideRandomizedData()
             ];
         }, array_fill(0, 50, null));
     }
+
+    public function test_head_on_empty_list_is_undefined()
+    {
+        $this->setExpectedException(\BadMethodCallException::class, 'head of empty Listt');
+
+        Listt::mempty()->head();
+    }
+
+    public function test_head_extracts_first_element()
+    {
+        $this->forAll(
+            vector(10, choose(1, 1000))
+        )(
+            function ($sequence) {
+                $list = Listt::of($sequence);
+                $current = current($sequence);
+
+                $this->assertSame($current, $list->head());
+                $this->assertSame($current, $list->head());
+            }
+        );
+    }
+
+    public function test_tail_on_empty_list()
+    {
+        $this->setExpectedException(\BadMethodCallException::class, 'tail of empty Listt');
+
+        Listt::mempty()->tail();
+    }
+
+    public function test_tail_with_single_element_Listt()
+    {
+        $this->forAll(
+            vector(1, choose(1, 1000))
+        )(
+            function ($sequence) {
+                $this->assertTrue(Listt::of($sequence)->tail()->equals(Listt::mempty()));
+            }
+        );
+    }
+
+    public function test_tail_with_multiple_element_Listt()
+    {
+        $this->forAll(
+            vector(10, choose(1, 1000))
+        )(
+            function ($sequence) {
+                $list = Listt::of($sequence);
+                array_shift($sequence);
+
+                $this->assertEquals($sequence, $list->tail()->extract());
+            }
+        );
+    }
 }