diff --git a/src/Functional/Each.php b/src/Functional/Each.php
index 3720a725..8cda140b 100644
--- a/src/Functional/Each.php
+++ b/src/Functional/Each.php
@@ -17,9 +17,14 @@
  * Iterates over a collection of elements, yielding each in turn to a callback function. Each invocation of $callback
  * is called with three arguments: (element, index, collection)
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return null
+ * @template K
+ * @template V
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):void $callback
+ *
+ * @return void
+ *
  * @no-named-arguments
  */
 function each($collection, callable $callback)
diff --git a/src/Functional/Every.php b/src/Functional/Every.php
index e4d8ff62..c4c0ec12 100644
--- a/src/Functional/Every.php
+++ b/src/Functional/Every.php
@@ -17,9 +17,14 @@
  * Returns true if every value in the collection passes the callback truthy test. Opposite of Functional\none().
  * Callback arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable|null $callback
+ * @template K
+ * @template V
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):bool $callback
+ *
  * @return bool
+ *
  * @no-named-arguments
  */
 function every($collection, callable $callback = null)
diff --git a/src/Functional/Filter.php b/src/Functional/Filter.php
index 46e09781..785449c0 100644
--- a/src/Functional/Filter.php
+++ b/src/Functional/Filter.php
@@ -16,9 +16,14 @@
 /**
  * Alias of Functional\select()
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return array
+ * @template K
+ * @template V
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):bool $callback
+ *
+ * @return array<K,V>
+ *
  * @no-named-arguments
  */
 function filter($collection, callable $callback)
diff --git a/src/Functional/First.php b/src/Functional/First.php
index 87db945e..1e868a2a 100644
--- a/src/Functional/First.php
+++ b/src/Functional/First.php
@@ -18,9 +18,13 @@
  * function returns as soon as it finds an acceptable element, and doesn't traverse the entire collection. Callback
  * arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return mixed
+ * @template T
+ *
+ * @param iterable<T> $collection
+ * @param null|callable(T):bool $callback
+ *
+ * @return  ($collection is non-empty-array ? ($callback is null ? T : T|null) : T|null)
+ *
  * @no-named-arguments
  */
 function first($collection, callable $callback = null)
diff --git a/src/Functional/FlatMap.php b/src/Functional/FlatMap.php
index 6a022f49..1a4f5d0f 100644
--- a/src/Functional/FlatMap.php
+++ b/src/Functional/FlatMap.php
@@ -24,9 +24,14 @@
  * then flat_map(collection, callback) will return [1,2,3,[4]]
  * while flatten(map(collection, callback)) will return [1,2,3,4]
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return array
+ * @template K
+ * @template V
+ * @template V2
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):(V2|iterable<V2>) $callback
+ *
+ * @return array<K,V2>
  * @no-named-arguments
  */
 function flat_map($collection, callable $callback)
diff --git a/src/Functional/Id.php b/src/Functional/Id.php
index b7de88dc..a1153b2f 100644
--- a/src/Functional/Id.php
+++ b/src/Functional/Id.php
@@ -13,8 +13,12 @@
 /**
  * Return value itself, without any modifications.
  *
- * @param mixed $value
- * @return mixed
+ * @template T
+ *
+ * @param T $value
+ *
+ * @return T
+ *
  * @no-named-arguments
  */
 function id($value)
diff --git a/src/Functional/Last.php b/src/Functional/Last.php
index 8989f945..ccb0d9d2 100644
--- a/src/Functional/Last.php
+++ b/src/Functional/Last.php
@@ -17,9 +17,13 @@
  * Looks through each element in the collection, returning the last one that passes a truthy test (callback).
  * Callback arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return mixed
+ * @template T
+ *
+ * @param iterable<T> $collection
+ * @param null|callable(T):bool $callback
+ *
+ * @return  T|null
+ *
  * @no-named-arguments
  */
 function last($collection, callable $callback = null)
diff --git a/src/Functional/Map.php b/src/Functional/Map.php
index 1bd577b3..2648f8af 100644
--- a/src/Functional/Map.php
+++ b/src/Functional/Map.php
@@ -17,9 +17,15 @@
  * Produces a new array of elements by mapping each element in collection through a transformation function (callback).
  * Callback arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return array
+ * @template K
+ * @template V
+ * @template V2
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):V2 $callback
+ *
+ * @return array<K,V2>
+ *
  * @no-named-arguments
  */
 function map($collection, callable $callback)
diff --git a/src/Functional/ReduceLeft.php b/src/Functional/ReduceLeft.php
index bce30c09..39b482dc 100644
--- a/src/Functional/ReduceLeft.php
+++ b/src/Functional/ReduceLeft.php
@@ -14,10 +14,16 @@
 use Traversable;
 
 /**
- * @param Traversable|array $collection
- * @param callable $callback
- * @param mixed $initial
- * @return mixed
+ * @template K
+ * @template V
+ * @template V2
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>,V2):V2 $callback
+ * @param V2 $initial
+ *
+ * @return V2
+ *
  * @no-named-arguments
  */
 function reduce_left($collection, callable $callback, $initial = null)
diff --git a/src/Functional/Reindex.php b/src/Functional/Reindex.php
index ba6cbdf9..58f9addc 100644
--- a/src/Functional/Reindex.php
+++ b/src/Functional/Reindex.php
@@ -17,9 +17,15 @@
  * Produces a new array of elements by assigning the values to keys generated by a transformation function (callback).
  * Callback arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @return array
+ * @template K
+ * @template V
+ * @template K2
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):K2 $callback
+ *
+ * @return array<K2,V>
+ *
  * @no-named-arguments
  */
 function reindex($collection, callable $callback)
diff --git a/src/Functional/Select.php b/src/Functional/Select.php
index 93420357..8a5523e7 100644
--- a/src/Functional/Select.php
+++ b/src/Functional/Select.php
@@ -17,9 +17,14 @@
  * Looks through each element in the list, returning an array of all the elements that pass a truthy test (callback).
  * Opposite is Functional\reject(). Callback arguments will be element, index, collection
  *
- * @param Traversable|array $collection
- * @param callable|null $callback
- * @return array
+ * @template K
+ * @template V
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):bool $callback
+ *
+ * @return array<K,V>
+ *
  * @no-named-arguments
  */
 function select($collection, callable $callback = null)
diff --git a/src/Functional/Some.php b/src/Functional/Some.php
index df27e0a8..ac38a706 100644
--- a/src/Functional/Some.php
+++ b/src/Functional/Some.php
@@ -17,9 +17,14 @@
  * Returns true if some of the elements in the collection pass the callback truthy test. Short-circuits and stops
  * traversing the collection if a truthy element is found. Callback arguments will be value, index, collection
  *
- * @param Traversable|array $collection
- * @param callable|null $callback
+ * @template K
+ * @template V
+ *
+ * @param iterable<K,V> $collection
+ * @param callable(V,K,iterable<K,V>):bool $callback
+ *
  * @return bool
+ *
  * @no-named-arguments
  */
 function some($collection, callable $callback = null)
diff --git a/src/Functional/Sum.php b/src/Functional/Sum.php
index e0f478b9..d1deed5e 100644
--- a/src/Functional/Sum.php
+++ b/src/Functional/Sum.php
@@ -16,9 +16,14 @@
 /**
  * Takes a collection and returns the sum of the elements
  *
- * @param Traversable|array $collection
- * @param integer|float $initial
- * @return integer|float
+ * @template K
+ * @template V of int|float
+ *
+ * @param iterable<K,V> $collection
+ * @param V $initial
+ *
+ * @return V
+ *
  * @no-named-arguments
  */
 function sum($collection, $initial = 0)
diff --git a/src/Functional/Unique.php b/src/Functional/Unique.php
index 656ac2be..1607a221 100644
--- a/src/Functional/Unique.php
+++ b/src/Functional/Unique.php
@@ -16,10 +16,15 @@
 /**
  * Returns an array of unique elements
  *
- * @param Traversable|array $collection
- * @param callable $callback
- * @param bool $strict
- * @return array
+ * @template K
+ * @template V
+ * @template D
+ *
+ * @param iterable<K,V> $collection
+ * @param null|callable(V,K,iterable<K,V>):D $callback
+ *
+ * @return array<K,V>
+ *
  * @no-named-arguments
  */
 function unique($collection, callable $callback = null, $strict = true)
diff --git a/src/Functional/With.php b/src/Functional/With.php
index 9e4532e5..234c0647 100644
--- a/src/Functional/With.php
+++ b/src/Functional/With.php
@@ -15,11 +15,18 @@
 /**
  * Invoke a callback on a value if the value is not null
  *
- * @param mixed $value
- * @param callable $callback
+ * @template V
+ * @template V2
+ * @template V3
+ * @template V4
+ *
+ * @param V|null|callable():V4 $value
+ * @param callable(V):V2 $callback
  * @param bool $invokeValue Set to false to not invoke $value if it is a callable. Will be removed in 2.0
- * @param mixed $default The default value to return if $value is null
- * @return mixed
+ * @param V3 $default The default value to return if $value is null
+ *
+ * @return ($value is null ? V3 : ($value is callable ? V4 : V2))
+ *
  * @no-named-arguments
  */
 function with($value, callable $callback, $invokeValue = true, $default = null)