diff --git a/src/Collection/GenericList.php b/src/Collection/GenericList.php
index d49c1c5..9425182 100644
--- a/src/Collection/GenericList.php
+++ b/src/Collection/GenericList.php
@@ -76,6 +76,13 @@ public function map(callable $mapper): self
         return new Cons($mapper($this->head()), $this->tail()->map($mapper));
     }
 
+    /**
+     * @template U
+     *
+     * @param callable(T): Traversable<U> $mapper
+     *
+     * @return GenericList<U>
+     */
     public function flatMap(callable $mapper)
     {
         $list = self::empty();
@@ -224,6 +231,9 @@ public function reverse(): self
         return $list;
     }
 
+    /**
+     * @return GenericList<T>
+     */
     public function appendAll(Traversable $elements)
     {
         if ($elements->isEmpty()) {
@@ -233,6 +243,9 @@ public function appendAll(Traversable $elements)
         return self::ofAll($elements)->prependAll($this);
     }
 
+    /**
+     * @return GenericList<T>
+     */
     public function prependAll(Traversable $elements)
     {
         if ($this->isEmpty()) {
diff --git a/src/Collection/Stream.php b/src/Collection/Stream.php
index 786f548..878853e 100644
--- a/src/Collection/Stream.php
+++ b/src/Collection/Stream.php
@@ -174,6 +174,13 @@ public function map(callable $mapper): self
         return new Cons($mapper($this->head()), function () use ($mapper) {return $this->tail()->map($mapper); });
     }
 
+    /**
+     * @template U
+     *
+     * @param callable(T): Traversable<U> $mapper
+     *
+     * @return Stream<U>
+     */
     public function flatMap(callable $mapper)
     {
         $stream = self::empty();
@@ -292,6 +299,9 @@ public function prepend($element)
         return new Cons($element, function () {return $this; });
     }
 
+    /**
+     * @return Stream<T>
+     */
     public function prependAll(Traversable $elements)
     {
         if ($elements->isEmpty()) {
diff --git a/src/Collection/Stream/Cons.php b/src/Collection/Stream/Cons.php
index 7536b6f..4831a67 100644
--- a/src/Collection/Stream/Cons.php
+++ b/src/Collection/Stream/Cons.php
@@ -71,6 +71,9 @@ public function iterator(): Iterator
         return new StreamIterator($this);
     }
 
+    /**
+     * @return Stream<T>
+     */
     public function append($element)
     {
         return new Cons($this->head, function () use ($element) {
@@ -78,6 +81,9 @@ public function append($element)
         });
     }
 
+    /**
+     * @return Stream<T>
+     */
     public function appendAll(Traversable $elements)
     {
         if ($elements->isEmpty()) {
diff --git a/src/Collection/Stream/EmptyStream.php b/src/Collection/Stream/EmptyStream.php
index 71986a1..656c098 100644
--- a/src/Collection/Stream/EmptyStream.php
+++ b/src/Collection/Stream/EmptyStream.php
@@ -51,11 +51,17 @@ public function iterator(): Iterator
         return Iterator::empty();
     }
 
+    /**
+     * @return Stream<T>
+     */
     public function append($element)
     {
         return Stream::of($element);
     }
 
+    /**
+     * @return Stream<T>
+     */
     public function appendAll(Traversable $elements)
     {
         if ($elements->isEmpty()) {