PEP 677: Clarify support for PEP 646 Unpack/* (#2198)

pep-0677.rst

@@ -450,7 +450,8 @@ Here are our proposed changes to the `Python Grammar
 
 
 If PEP 646 is accepted, we intend to include support for unpacked
-types by modifying the grammar for
+types in two ways. To support the "star-for-unpack" syntax proposed in
+PEP 646, we will modify the grammar for
 ``callable_type_positional_argument`` as follows::
 
     callable_type_positional_argument:
@@ -459,11 +460,21 @@ types by modifying the grammar for
         | '*' expression ','
         | '*' expression &')'
 
+With this change, a type of the form ``(int, *Ts) -> bool`` should
+evaluate the AST form::
+
+    CallableType(
+        ArgumentsList(Name("int"), Starred(Name("Ts")),
+        Name("bool")
+    )
+
+and be treated by type checkers as equivalent to
+``Callable[[int, Unpack[Ts]], bool]``.
+
 
 Implications of the Grammar
 ---------------------------
 
-
 Precedence of ->
 ~~~~~~~~~~~~~~~~