--- /dev/null
+##############################################################################
+# $URL: http://perlcritic.tigris.org/svn/perlcritic/trunk/Perl-Critic/lib/Perl/Critic/Policy/ControlStructures/ProhibitNegativeExpressionsInUnlessAndUntilConditions.pm $
+# $Date: 2008-07-03 10:19:10 -0500 (Thu, 03 Jul 2008) $
+# $Author: clonezone $
+# $Revision: 2489 $
+##############################################################################
+
+package Perl::Critic::Policy::ControlStructures::ProhibitNegativeExpressionsInUnlessAndUntilConditions;
+
+use 5.006001;
+use strict;
+use warnings;
+use English qw(-no_match_vars);
+use Readonly;
+
+use Perl::Critic::Utils qw< :characters :severities :classification hashify >;
+
+use base 'Perl::Critic::Policy';
+
+our $VERSION = '1.088';
+
+#-----------------------------------------------------------------------------
+
+Readonly::Scalar my $EXPL => [99];
+
+#-----------------------------------------------------------------------------
+
+sub supported_parameters { return qw< > }
+sub default_severity { return $SEVERITY_MEDIUM }
+sub default_themes { return qw( core maintenance ) }
+sub applies_to { return 'PPI::Token::Word' }
+
+#-----------------------------------------------------------------------------
+
+sub violates {
+ my ( $self, $token, undef ) = @_;
+
+ return if $token ne 'until' && $token ne 'unless';
+
+ return if is_hash_key($token);
+ return if is_subroutine_name($token);
+ return if is_method_call($token);
+ return if is_included_module_name($token);
+
+ return
+ map
+ { $self->_violation_for_operator( $_, $token ) }
+ _get_negative_operators( $token );
+}
+
+#-----------------------------------------------------------------------------
+
+sub _get_negative_operators {
+ my ($token) = @_;
+
+ my @operators;
+ foreach my $element ( _get_condition_elements($token) ) {
+ if ( $element->isa('PPI::Node') ) {
+ my $operators = $element->find( \&_is_negative_operator );
+ if ($operators) {
+ push @operators, @{$operators};
+ }
+ }
+ else {
+ if ( _is_negative_operator( undef, $element ) ) {
+ push @operators, $element;
+ }
+ }
+ }
+
+ return @operators;
+}
+
+#-----------------------------------------------------------------------------
+
+sub _get_condition_elements {
+ my ($token) = @_;
+
+ my $statement = $token->statement();
+ return if not $statement;
+
+ if ($statement->isa('PPI::Statement::Compound')) {
+ my $condition = $token->snext_sibling();
+
+ return if not $condition;
+ return if not $condition->isa('PPI::Structure::Condition');
+
+ return ( $condition );
+ }
+
+ my @condition_elements;
+ my $element = $token;
+ while (
+ $element = $element->snext_sibling()
+ and $element ne $SCOLON
+ ) {
+ push @condition_elements, $element;
+ }
+
+ return @condition_elements;
+}
+
+#-----------------------------------------------------------------------------
+
+Readonly::Hash my %NEGATIVE_OPERATORS => hashify(
+ qw/
+ ! not
+ !~ ne !=
+ < > <= >= <=>
+ lt gt le ge cmp
+ /
+);
+
+sub _is_negative_operator {
+ my (undef, $element) = @_;
+
+ return
+ $element->isa('PPI::Token::Operator')
+ && $NEGATIVE_OPERATORS{$element};
+}
+
+#-----------------------------------------------------------------------------
+
+sub _violation_for_operator {
+ my ($self, $operator, $control_structure) = @_;
+
+ return
+ $self->violation(
+ qq<Found "$operator" in condition for an "$control_structure">,
+ $EXPL,
+ $control_structure,
+ );
+}
+
+1;
+
+#-----------------------------------------------------------------------------
+
+__END__
+
+=pod
+
+=for stopwords
+
+=head1 NAME
+
+Perl::Critic::Policy::ControlStructures::ProhibitNegativeExpressionsInUnlessAndUntilConditions - Don't use operators like C<not>, C<!~>, and C<le> within C<until> and C<unless>.
+
+=head1 AFFILIATION
+
+This Policy is part of the core L<Perl::Critic> distribution.
+
+
+=head1 DESCRIPTION
+
+ until ($foo ne 'blah') { #not ok
+ ...
+ }
+
+ while ($foo eq 'blah') { #ok
+ ...
+ }
+
+A number of people have problems figuring out the meaning of doubly
+negated expressions. C<unless> and C<until> are both negative
+constructs, so any negative (e.g. C<!~>) or reversible operators (e.g.
+C<le>) included in their conditional expressions are double negations.
+Conway considers the following operators to be difficult to understand
+within C<unless> and C<until>:
+
+ ! not
+ !~ ne !=
+ < > <= >= <=>
+ lt gt le ge cmp
+
+
+
+=head1 CONFIGURATION
+
+This Policy is not configurable except for the standard options.
+
+
+=head1 SEE ALSO
+
+L<Perl::Critic::Policy::ControlStructures::ProhibitUnlessBlocks>
+
+=head1 AUTHOR
+
+Elliot Shank C<< <perl@galumph.com> >>
+
+=head1 COPYRIGHT
+
+Copyright (c) 2007-2008 Elliot Shank. All rights reserved.
+
+This program is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself. The full text of this license
+can be found in the LICENSE file included with this module.
+
+=cut
+
+# Local Variables:
+# mode: cperl
+# cperl-indent-level: 4
+# fill-column: 78
+# indent-tabs-mode: nil
+# c-indentation-style: bsd
+# End:
+# ex: set ts=8 sts=4 sw=4 tw=78 ft=perl expandtab shiftround :
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