#!/usr/bin/env perl
#
#   parse_config_file.pl - a quickie parser for <tag>: <value> config files
#
use strict;
use warnings;
use Marpa::R2;
use Data::Dump qw(pp);

my $stuff = <<'EOGrammar';
:default ::= action => [ values ]
lexeme default = latm => 1

ConfigFile ::= Line ConfigFile         action => return_result
ConfigFile ::=                         action => return_result

Line ::= Tag COLON Value EOL           action => add_config_value
     |   EOL

Tag ::= START_CHAR Tag_remainder       action => add_remainder
Tag_remainder ::=
    TAG_CHAR Tag_remainder             action => add_remainder
    | TAG_CHAR                         action => ::first

Value ::= START_CHAR Value_remainder   action => add_remainder
Value_remainder ::=
    VAL_CHAR Value_remainder           action => add_remainder
    | VAL_CHAR                         action => ::first

####
# Token definitions
####

:discard ~ WHITESPACE
WHITESPACE ~ [\r\t ]+

# Delimiter between the tag and the value
COLON ~ [:]

# End of line marker
EOL ~ [\n]

# Starting character of a tag/value
START_CHAR ~ [^:\s]

# Legal characters in a tag after the starting character
TAG_CHAR ~ [^:\n]

# After the starting character, a value can have any character but line end
VAL_CHAR ~ [^\n]

EOGrammar

my $grammar = Marpa::R2::Scanless::G->new({ source=> \$stuff });
my $input = join("", <DATA>);

# Note: Right-hand-side is wrapped in ${...} because we're returning a
# reference to a hash reference.  (Not as useful as a plain hashref)
my $config = ${$grammar->parse( \$input, 'ConfigFileActions' )};

print "Daily mission: ", $config->{'What are we doing today Brain'}, "\n";
print "Location: ", $config->{where}, "\n\n";

print "All configuration data: ", pp($config), "\n";

sub ConfigFileActions::add_config_value {
    # Add the tag / value combination to the result hash
    my ($result, $tag, $colon, $val) = @_;
    $result->{$tag} = $val;
    return $result;
}

sub ConfigFileActions::add_remainder {
    # Append character to the tag/val string
    my ($context, $char, $rest) = @_;
    return join("", $char, $rest);
}

sub ConfigFileActions::return_result {
    # Final result of a top-level production is to return the
    # hash reference we've been building
    my ($context, undef) = @_;
    return $context;
}

__DATA__
where: October
foo: bar
baz: 1234+54q - bar bar
who: bob
Some other parameter: 42
What are we doing today Brain: Same thing we do every day Pinky

##</code><code>##

$ perl parse_cfg_file.pl
Daily mission: Same thing we do every day Pinky
Location: October

All configuration data: {
  "baz" => "1234+54q - bar bar",
  "foo" => "bar",
  "Some other parameter" => 42,
  "What are we doing today Brain" => "Same thing we do every day Pinky",
  "where" => "October",
  "who" => "bob",
}