Functional\drop test + implementation

src/Functional/listt.php

@@ -9,6 +9,7 @@
 
 const fromIterable = 'Widmogrod\Functional\fromIterable';
 
+// TODO extract
 class SnapshotIterator extends \IteratorIterator
 {
     private $inMemoryValid;

src/Functional/sublist.php

@@ -11,18 +11,22 @@
  * take n, applied to a list xs, returns the prefix of xs of length n, or xs itself if n > length xs:
  *
  * @param int $n
- * @param Listt $a
+ * @param Listt $xs
  * @return Listt
  */
-function take(int $n, Listt $a = null)
+function take(int $n, Listt $xs = null)
 {
-    return curryN(2, function (int $n, Listt $a): Listt {
+    return curryN(2, function (int $n, Listt $xs): Listt {
         if ($n < 1) {
             return fromNil();
         }
 
+        if ($n > length($xs)) {
+            return $xs;
+        }
+
         try {
-            return prepend(head($a), take($n - 1, tail($a)));
+            return prepend(head($xs), take($n - 1, tail($xs)));
         } catch (EmptyListError $e) {
             return fromNil();
         }
@@ -33,10 +37,27 @@ function take(int $n, Listt $a = null)
  * drop :: Int -> [a] -> [a]
  *
  * drop n xs returns the suffix of xs after the first n elements, or [] if n > length xs:
+ * @param int $n
+ * @param Listt $xs
+ * @return Listt
  */
-function drop()
+function drop(int $n, Listt $xs = null)
 {
-    // TODO
+    return curryN(2, function (int $n, Listt $xs): Listt {
+        if ($n < 1) {
+            return $xs;
+        }
+
+        if ($n > length($xs)) {
+            return fromNil();
+        }
+
+        try {
+            return drop($n - 1, tail($xs));
+        } catch (EmptyListError $e) {
+            return fromNil();
+        }
+    })(...func_get_args());
 }
 
 /**

test/Functional/DropTest.php

@@ -0,0 +1,61 @@
+<?php
+
+namespace test\Functional;
+
+use Widmogrod\Primitive\Listt;
+use function Widmogrod\Functional\drop;
+use function Widmogrod\Functional\fromIterable;
+use function Widmogrod\Functional\fromNil;
+
+class DropTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @dataProvider provideData
+     */
+    public function test_it(
+        Listt $a,
+        int $n,
+        Listt $expected
+    ) {
+        $result = drop($n, $a);
+
+        $r = print_r($result->extract(), true);
+        $e = print_r($expected->extract(), true);
+
+        $this->assertTrue(
+            $result->equals($expected),
+            "$e != $r"
+        );
+    }
+
+    public function provideData()
+    {
+        return [
+            'should return empty list from when input is empty list' => [
+                '$a' => fromNil(),
+                '$n' => 1,
+                '$expected' => fromNil(),
+            ],
+            'should provided list when n is zero' => [
+                '$a' => fromIterable([1, 2, 3, 4, 5]),
+                '$n' => 0,
+                '$expected' => fromIterable([1, 2, 3, 4, 5]),
+            ],
+            'should provided list when n is negative' => [
+                '$a' => fromIterable([1, 2, 3, 4, 5]),
+                '$n' => random_int(-1000, -1),
+                '$expected' => fromIterable([1, 2, 3, 4, 5]),
+            ],
+            'should return part of finite list' => [
+                '$a' => fromIterable([1, 2, 3, 4, 5]),
+                '$n' => 3,
+                '$expected' => fromIterable([4, 5]),
+            ],
+            'should return nil list when drop more than in the list' => [
+                '$a' => fromIterable([1, 2, 3, 4, 5]),
+                '$n' => 3000,
+                '$expected' => fromNil(),
+            ],
+        ];
+    }
+}