NAME
Marpa::R3::Changes - Differences between Marpa::R2 and Marpa::R3
About this document
This document describes the incompatible differences between Marpa::R2 and Marpa::R3. (Differences that do not give rise to incompatibility are outside of its scope.) It is intended for readers already familiar with Marpa::R2, who are writing new applications for Marpa::R3, and for readers migrating Marpa::XS applications and tools to Marpa::R3.
Changes
Semantics moved from recognizer to grammar
In Marpa::R2, the semantics was not finally settled until the $recce->value() call. In Marpa::R3, semantics will be fully settled in the grammar.
Options moved from recognizer to grammar
The exhaustion, ranking_method, rejection, semantics_package, and trace_actions named arguments are grammar options in Marpa::R3. They were recognizer name arguments in Marpa::R2,
Actions that are Perl names must resolve to subroutines
It was a little noticed feature of Marpa::R2, that actions specified as Perl names (like "My_Action::doit") could resolve to scalars. In Marpa::R3 they must resolve to Perl subroutines.
Newlines now obey Perl standards
In Marpa::R3 newlines are defined as in Perl. In Marpa::R2 newlines were recognized according to the Unicode standard, which was a superset including UNIX and Windows newlines.
The Stuifzand interface (PSIF) has been removed
The Stuifzand interface (PSIF), and its documentation, have been removed. Important in the development of Marpa, it now has little or now usage.
The Thin interface (THIF) has been removed.
The THIF was a "thin" Perl interface. It has been removed.
The NAIF has been removed
The NAIF was an older interface using hashes of named variables, instead of a DSL. It has been removed.
LATM is now the default
[name, values] is now the default action
Unicode now works in the SLIF DSL
New method g1_input_span
Context::location is now Context::g1_range
New context variable, Context::g1_span
Marpa::R2::Scanless::G named arguments removed in Marpa::R3
The actions, action_object, default_action and default_empty_action named arguments of Marpa::R2::Scanless::G named arguments have been removed in Marpa::R3.
New Marpa::R3::Scanless::G methods
Several new methods have been added as accessors for L0 grammars:
Marpa::R2::Scanless::G::l0_symbol_dsl_form()Marpa::R2::Scanless::G::l0_rule_expand()Marpa::R2::Scanless::G::l0_rule_ids()Marpa::R2::Scanless::G::l0_rule_show()Marpa::R2::Scanless::G::l0_symbol_display_form()Marpa::R2::Scanless::G::l0_symbol_ids()Marpa::R2::Scanless::G::l0_symbol_name()Marpa::R2::Scanless::G::l0_show_rules()Marpa::R2::Scanless::G::l0_show_symbols()
Marpa::R2::Scanless::G methods removed in Marpa::R3
The Marpa::R2::Scanless::G::g0_rule() method, the Marpa::R2::Scanless::G::g0_rule_ids() method, the Marpa::R2::Scanless::G::g1_rule_ids() method, and the Marpa::R2::Scanless::G::rule() method, discouraged in Marpa::R2, have been eliminated in Marpa::R3.
The Marpa::R2::Scanless::G::symbol_description() method has been removed.
Marpa::R2::Scanless::G methods changed in Marpa::R3
The following methods have been changed:
Marpa::R2::Scanless::G::symbol_dsl_form()Marpa::R2::Scanless::G::rule_expand()Marpa::R2::Scanless::G::rule_ids()Marpa::R2::Scanless::G::rule_show()Marpa::R2::Scanless::G::symbol_display_form()Marpa::R2::Scanless::G::symbol_ids()Marpa::R2::Scanless::G::symbol_name()Marpa::R2::Scanless::G::show_rules()Marpa::R2::Scanless::G::show_symbols()
They no longer take an argument indicating the subgrammar -- instead they always return result for the G1 grammar. New methods have been added to return results for the L0 grammar. For these, see "New Marpa::R3::Scanless::G methods".
Marpa::R2::Scanless::R methods renamed in Marpa::R3
For historical reasons, the methods dealing with input and G1 parse location in Marpa::R2 often had unhelpful or misleading names. In Marpa::R3 an attempt is being made to name methods dealing with G1 and input parse location consistently, and to ensure that the G1 variants have g1 somewhere in their name. Accordingly, $slr->substring() has been renamed $slr->g1_literal(); and $slr->current_g1_location() is now $slr->g1_pos().
Marpa::R2::Scanless::R methods removed in Marpa::R3
The Marpa::R2::Scanless::R::event() method, Marpa::R2::Scanless::R::last_completed_range() method, Marpa::R2::Scanless::R::pause_lexeme() method, and the Marpa::R2::Scanless::R::range_to_string() method, discouraged in Marpa::R2, have been eliminated in Marpa::R3.
The per-parse constructor has been elminated
In Marpa::R2, if the semantics package has a new() method, that method was used as the constructor of the per-parse object. In Marpa::R3, there is no per-parse constructor.
The per-parse argument never affects the semantics package
As of Marpa::R3, the per-parse argument has no effect on the semantics package. In Marpa::R2, if the c<semantics_package> named argument was not used and the per-parse argument was blessed, then the package into which the per-parse argument was blessed became the semantics package.
The semantic closure now always receives exactly 2 arguments
Under Marpa::R2, the semantic closure received a varying number of arguments, depending on circumstances. Under Marpa::R3, the semantic closure always receives exactly 2 arguments. The first argument is the per-parse object. The second argument is a reference to an array containing the values of the child nodes, in lexical order. If there were no child nodes visible to the semantics, then the second argument is an empty array.
Under Marpa::R2, the events() method returned events in a specified order, by type of event. Under Marpa::R3, the order of events returned by the events() method is completely arbitrary.
COPYRIGHT AND LICENSE
Marpa::R3 is Copyright (C) 2016, Jeffrey Kegler.
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl 5.10.1. For more details, see the full text
of the licenses in the directory LICENSES.
This program is distributed in the hope that it will be
useful, but without any warranty; without even the implied
warranty of merchantability or fitness for a particular purpose.