Add Enumerator::_Each interface

core/enumerator.rbs

@@ -130,6 +130,13 @@
 class Enumerator[unchecked out Elem, out Return] < Object
   include Enumerable[Elem]
 
+  # A convenience interface for `each` with optional block
+  #
+  interface _Each[out E, out R]
+    def each: () { (E) -> void } -> R
+            | () -> Enumerator[E, R]
+  end
+
   # <!--
   #   rdoc-file=enumerator.c
   #   - Enumerator.produce(initial = nil) { |prev| block } -> enumerator

docs/syntax.md

@@ -64,7 +64,7 @@ Interface type denotes _type of a value which can be a subtype of the interface_
 
 ```rbs
 _ToS                          # _ToS interface
-::MyApp::_Each[String]        # Interface name with namespace and type application
+::Enumerator::_Each[String]   # Interface name with namespace and type application
 ```
 
 ### Alias type