Experiment with tuple notation

src/Data/Tuple.php

@@ -12,7 +12,8 @@
  * @implements EqInstance<Tuple<A,B>>
  */
 class Tuple implements
-    EqInstance
+    EqInstance,
+    \ArrayAccess
 {
     /**
      * (,) :: a -> b -> (a, b)
@@ -155,4 +156,40 @@ public function notEquals(EqInstance $other): bool
     {
         return !$this->equals($other);
     }
+
+    public function offsetExists($offset)
+    {
+        return $offset == 0 || $offset == 1;
+    }
+
+    public function offsetGet($offset)
+    {
+        if ($offset === 0) {
+            return $this->fst();
+        }
+
+        if ($offset === 1) {
+            return $this->snd();
+        }
+
+        return null;
+    }
+
+    public function offsetSet($offset, $value)
+    {
+        if ($offset == 0) {
+            $this->a = $value;
+        }
+
+        if ($offset == 1) {
+            $this->b = $value;
+        }
+
+        throw new \Exception('Unknown offset');
+    }
+
+    public function offsetUnset($offset)
+    {
+        throw new \Exception('Cannot unset!');
+    }
 }

tests/TupleTest.php

@@ -17,6 +17,26 @@ public function testCanCreateTuple(): void
         $this->assertTupleIs(123, "hello world", $tuple);
     }
 
+    public function testCanUnwrap(): void
+    {
+        // todo: is there a better implementation instead of ArrayAccess here?
+        $tuple = Tuple::new(123, "hello world");
+        [$fst, $snd] = $tuple;
+
+        $this->assertEquals(123, $fst);
+        $this->assertEquals("hello world", $snd);
+    }
+
+    public function testCanGetNewTuple(): void
+    {
+        // todo: no remove this. just make new tuples.
+        $tuple = Tuple::new(123, "hello world");
+        $tuple[0] = 'one';
+        $tuple[1] = 'two';
+
+        $this->assertTupleIs('one', 'two', $tuple);
+    }
+
     public function testCanSwapTupleValues(): void
     {
         $tuple = Tuple::new(123, "hello world")->swap();