PEP 622: Rename 'named sub-pattern' to 'walrus pattern' (#1482)

pep-0622.rst

@@ -139,7 +139,8 @@ A simplified, approximate grammar for the proposed syntax is::
   match_stmt: "match" expression ':' NEWLINE INDENT case_block+ DEDENT
   case_block: "case" pattern [guard] ':' block
   guard: 'if' expression
-  pattern: NAME ':=' or_pattern | or_pattern
+  pattern: walrus_pattern | or_pattern
+  walrus_pattern: NAME ':=' or_pattern
   or_pattern: closed_pattern ('|' closed_pattern)*
   closed_pattern:
       | literal_pattern
@@ -507,22 +508,20 @@ is a ``SyntaxError`` and ``1 | 2 if 3 | 4`` will be parsed as
 ``(1 | 2) if (3 | 4)``.
 
 
-.. _named:
+Walrus patterns
+---------------
 
-Named sub-patterns
-------------------
-
-It is often useful to match a sub-pattern *and* to bind the corresponding
+It is often useful to match a sub-pattern *and* bind the corresponding
 value to a name. For example, it can be useful to write more efficient
-matches, or simply to avoid repetition. To simplify such cases, a capture pattern
-can be combined with another arbitrary pattern using named sub-patterns of
-the form ``name := pattern``. For example::
+matches, or simply to avoid repetition. To simplify such cases, any pattern
+(other than the walrus pattern itself) can be preceded by a name and
+the walrus operator (``:=``). For example::
 
   match get_shape():
       case Line(start := Point(x, y), end) if start == end:
           print(f"Zero length line at {x}, {y}")
 
-Note that the capture pattern used in the named sub-pattern can be used in
+The name on the left of the walrus operator can be used in a guard, in
 the match suite, or after the match statement.  However, the name will
 *only* be bound if the sub-pattern succeeds.  Another example::
 
@@ -1728,7 +1727,8 @@ Other notation used beyond standard EBNF:
   case_block: "case" patterns [guard] ':' block
   guard: 'if' named_expression
   patterns: value_pattern ',' [values_pattern] | pattern
-  pattern: NAME ':=' or_pattern | or_pattern
+  pattern: walrus_pattern | or_pattern
+  walrus_pattern: NAME ':=' or_pattern
   or_pattern: '|'.closed_pattern+
   closed_pattern:
       | capture_pattern