Marpa::R2::Scanless::R - Scanless interface recognizers
my $recce = Marpa::R2::Scanless::R->new( { grammar => $grammar } ); my $self = bless { grammar => $grammar }, 'My_Actions'; $self->{recce} = $recce; local $My_Actions::SELF = $self; if ( not defined eval { $recce->read($p_input_string); 1 } ) { ## Add last expression found, and rethrow my $eval_error = $EVAL_ERROR; chomp $eval_error; die $self->show_last_expression(), "\n", $eval_error, "\n"; } ## end if ( not defined eval { $event_count = $recce->read...}) my $value_ref = $recce->value(); if ( not defined $value_ref ) { die $self->show_last_expression(), "\n", "No parse was found, after reading the entire input\n"; }
package My_Actions; our $SELF; sub new { return $SELF } sub do_parens { shift; return $_[1] } sub do_add { shift; return $_[0] + $_[2] } sub do_subtract { shift; return $_[0] - $_[2] } sub do_multiply { shift; return $_[0] * $_[2] } sub do_divide { shift; return $_[0] / $_[2] } sub do_pow { shift; return $_[0]**$_[2] } sub do_first_arg { shift; return shift; } sub do_script { shift; return join q{ }, @_ }
sub show_last_expression { my ($self) = @_; my $recce = $self->{recce}; my ( $start, $end ) = $recce->last_completed_range('Expression'); return 'No expression was successfully parsed' if not defined $start; my $last_expression = $recce->range_to_string( $start, $end ); return "Last expression successfully parsed was: $last_expression"; } ## end sub show_last_expression
This page is the reference document for the recognizer objects of Marpa's Scanless interface.
my $recce = Marpa::R2::Scanless::R->new( { grammar => $grammar } );
The new() method is the constructor for Scanless recognizers. An example of its use is above. The new() constructor accepts a hash of named arguments. The following named arguments are allowed:
new()
The new method is required to have a grammar named argument. Its value must be a Scanless grammar object.
new
grammar
If non-zero, traces the lexemes -- those tokens passed from the G0 parser to the G1 parser. This named argument is the best way to follow what the G0 parser is doing, but it is also very helpful for tracing the G1 parser.
This named argument is passed on to the G1 recognizer. See "trace_values" in Marpa::R2::Recognizer
The value is a file handle. Trace output and warning messages go to the trace file handle. By default the trace file handle is STDERR.
STDERR
my ( $start, $end ) = $recce->last_completed_range('Expression');
Given the name of a symbol, returns the start and end locations of most recent match. If there was more than one most recent match, it returns the longest. If there was no match, returns the empty array in array context and a Perl false in scalar context.
my $last_expression = $recce->range_to_string( $start, $end );
Given a start and an end location, returns the substring of the input string that is between the two.
$recce->read($p_input_string);
Given a pointer to an input string, parses it according to the grammar. Currently only a single call to read() is allowed for a scanless recognizer. On success, returns a non-negative integer. On failure, throws an exception.
read()
my $show_progress_output = $recce->show_progress();
Has the same effect as a show_progress() call on the G1 recognizer. See "show_progress()" in Marpa::R2::Recognizer.
show_progress()
my $value_ref = $recce->value();
Has the same effect as a value() call on the G1 recognizer. See "value()" in Marpa::R2::Recognizer.
value()
Copyright 2013 Jeffrey Kegler This file is part of Marpa::R2. Marpa::R2 is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Marpa::R2 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. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with Marpa::R2. If not, see http://www.gnu.org/licenses/.
To install Marpa::R2, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Marpa::R2
CPAN shell
perl -MCPAN -e shell install Marpa::R2
For more information on module installation, please visit the detailed CPAN module installation guide.