feat(filter): filters out falsy values without callable

Author: camillebaronnet

README.md

@@ -65,7 +65,7 @@ Full documentation with signatures and examples: **[docs/API.md](docs/API.md)**
 Lazy (Generator-based) unless noted as blocking.
 
 - [`map`](docs/API.md#map) — Apply a callback to each element
-- [`filter`](docs/API.md#filter) — Keep elements matching a predicate
+- [`filter`](docs/API.md#filter) — Keep elements matching a predicate (without callback: remove falsy values)
 - [`flatMap`](docs/API.md#flatmap) — Map then flatten one level
 - [`flatten`](docs/API.md#flatten) — Flatten one level of nested iterables
 - [`take`](docs/API.md#take) — Take the first N elements

docs/API.md

@@ -37,14 +37,18 @@ Applies `$fn` to each element. Receives `($value, $key)`. Preserves keys.
 ### `filter`
 
 ```php
-filter(callable $fn): Closure
+filter(?callable $fn = null): Closure
 ```
 
 Keeps elements where `$fn` returns `true`. Receives `($value, $key)`.
+Without callback, removes falsy values (`null`, `false`, `0`, `""`, `[]`) — like `array_filter()`.
 
 ```php
 [1, 2, 3, 4, 5] |> filter(fn(int $n) => $n > 3) |> toArray();
 // [4, 5]
+
+[1, 0, null, '', false, 2] |> filter() |> toArray();
+// [1, 2]
 ```
 
 ### `flatMap`

src/Transformations/filter.php

@@ -9,14 +9,15 @@
 
 /**
  * Keeps only elements that satisfy the predicate.
+ * Without argument, filters out falsy values (like array_filter).
  *
- * @param callable(mixed, mixed=): bool $fn ($value, $key)
+ * @param callable(mixed, mixed=): bool|null $fn ($value, $key)
  */
-function filter(callable $fn): Closure
+function filter(?callable $fn = null): Closure
 {
     return static function (iterable $items) use ($fn): Generator {
         foreach ($items as $key => $value) {
-            if ($fn($value, $key)) {
+            if ($fn ? $fn($value, $key) : $value) {
                 yield $value;
             }
         }

tests/FilterTest.php

@@ -32,6 +32,18 @@ public function testReturnsEmptyForNoMatch(): void
         self::assertSame([], filter(fn(int $n) => $n > 100)([1, 2, 3]) |> toArray());
     }
 
+    public function testWithoutCallbackFiltersFalsyValues(): void
+    {
+        $result = [1, 0, null, 'hello', '', false, 2, [], true] |> filter() |> toArray();
+
+        self::assertSame([1, 'hello', 2, true], $result);
+    }
+
+    public function testWithoutCallbackOnEmptyArray(): void
+    {
+        self::assertSame([], [] |> filter() |> toArray());
+    }
+
     public function testIsLazy(): void
     {
         $evaluated = 0;