Gist for blog post announcing Marpa's Scanless interface

gistfile1.pl

#!/usr/bin/perl
# Copyright 2012 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/.

# A example of the Scannerless interface, for a blog post

use 5.010;
use strict;
use warnings;
use English qw( -no_match_vars );
use Marpa::R2 2.038000;

my $grammar = Marpa::R2::Scanless::G->new(
    {   
        action_object  => 'My_Actions',
        default_action => 'do_first_arg',
        source          => \(<<'END_OF_SOURCE'),
:start ::= Script
Script ::= Expression+ separator => comma action => do_script
comma ~ [,]
Expression ::=
    Number
    | '(' Expression ')' action => do_parens assoc => group
   || Expression '**' Expression action => do_pow assoc => right
   || Expression '*' Expression action => do_multiply
    | Expression '/' Expression action => do_divide
   || Expression '+' Expression action => do_add
    | Expression '-' Expression action => do_subtract
Number ~ [\d]+

:discard ~ whitespace
whitespace ~ [\s]+
# allow comments
:discard ~ <hash comment>
<hash comment> ~ <terminated hash comment> | <unterminated
   final hash comment>
<terminated hash comment> ~ '#' <hash comment body> <vertical space char>
<unterminated final hash comment> ~ '#' <hash comment body>
<hash comment body> ~ <hash comment char>*
<vertical space char> ~ [\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
<hash comment char> ~ [^\x{A}\x{B}\x{C}\x{D}\x{2028}\x{2029}]
END_OF_SOURCE
    }
);

sub my_parser {
    my ( $grammar, $p_input_string ) = @_;

    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";
    }

    return ${$value_ref};

} ## end sub my_parser

my @tests = (
    [   '42*2+7/3, 42*(2+7)/3, 2**7-3, 2**(7-3)' =>
            qr/\A 86[.]3\d+ \s+ 126 \s+ 125 \s+ 16\z/xms
    ],
    [   '42*3+7, 42 * 3 + 7, 42 * 3+7' => qr/ \s* 133 \s+ 133 \s+ 133 \s* /xms
    ],
    [   '15329 + 42 * 290 * 711, 42*3+7, 3*3+4* 4' =>
            qr/ \s* 8675309 \s+ 133 \s+ 25 \s* /xms
    ],
);

for my $test (@tests) {
    my ( $input, $output_re ) = @{$test};
    my $value = my_parser( $grammar, \$input );
    $value =~ $output_re
        or die "Problem parsing $input\n",
        "  Value is $value\n",
        "  It was expected to, but did not match $output_re";
} ## end for my $test (@tests)

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

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