Author: lwall
Date: 2010-05-05 18:49:28 +0200 (Wed, 05 May 2010)
New Revision: 30551
Modified:
docs/Perl6/Spec/S05-regex.pod
docs/Perl6/Spec/S32-setting-library/Basics.pod
Log:
[S05] give overview of Perl patterns in terms of PEGs, and spec tiebreaking
explicitly
[Basics.pod] remove fossil 'proto object'
Modified: docs/Perl6/Spec/S05-regex.pod
===================================================================
--- docs/Perl6/Spec/S05-regex.pod 2010-05-05 14:14:08 UTC (rev 30550)
+++ docs/Perl6/Spec/S05-regex.pod 2010-05-05 16:49:28 UTC (rev 30551)
@@ -16,8 +16,8 @@
Created: 24 Jun 2002
- Last Modified: 5 apr 2010
- Version: 118
+ Last Modified: 5 May 2010
+ Version: 119
This document summarizes Apocalypse 5, which is about the new regex
syntax. We now try to call them I<regex> rather than "regular
@@ -34,6 +34,30 @@
In any case, when referring to recursive patterns within a grammar,
the terms I<rule> and I<token> are generally preferred over I<regex>.
+=head1 Overview
+
+In essence, Perl 6 natively implements Parsing Expression Grammars (PEGs)
+as an extension of regular expression notation. PEGs require that you
+provide a "pecking order" for ambiguous parses. Perl 6's packing order
+is determined by a multi-level tie-breaking test:
+
+ 1) Longest token matching: food\s+ beats foo by 2 or more positions
+ 2) Longest literal prefix: food\w* beats foo\w* by 1 position
+ 3) Declaration from most-derived grammar beats less-derived
+ 4) Within a given compilation unit, earlier declaration wins
+ 5) Declaration with least number of 'uses' wins
+
+Note that tiebreaker #5 can occur only when a grammar is monkey-patched
+from another compilation unit. Like #3, it privileges local declarations
+over distant ones.
+
+In addition to this pecking order, if any rule chosen under the pecking
+backtracks, the next best rule is chosen. That is, the pecking order
+determines a candidate list; just because one candidate is chosen does not
+mean the rest are thrown away. They may, however, be explicitly thrown away
+by an appropriate backtracking control (sometimes called a "cut" operator,
+but Perl6 has several of them, depending on how much you want to cut).
+
=head1 New match result and capture variables
The underlying match object is now available via the C<$/>
Modified: docs/Perl6/Spec/S32-setting-library/Basics.pod
===================================================================
--- docs/Perl6/Spec/S32-setting-library/Basics.pod 2010-05-05 14:14:08 UTC
(rev 30550)
+++ docs/Perl6/Spec/S32-setting-library/Basics.pod 2010-05-05 16:49:28 UTC
(rev 30551)
@@ -168,7 +168,7 @@
C<$by> or C<@by> for comparisons. C<@by> differs from C<$by>
in that each criterion is applied, in order, until a non-zero
(tie) result is achieved. If the values are not comparable,
-returns a proto C<Order> object that is undefined.
+returns an C<Order> type object that is undefined.
=item does
