#  You may distribute under the terms of either the GNU General Public License
#  or the Artistic License (the same terms as Perl itself)
#
#  (C) Paul Evans, 2022-2024 -- leonerd@leonerd.org.uk

package Syntax::Operator::Elem 0.10;

use v5.14;
use warnings;

use Carp;

use meta 0.003_002;
no warnings 'meta::experimental';

=encoding UTF-8

=head1 NAME

C<Syntax::Operator::Elem> - element-of-list operators

=head1 SYNOPSIS

On Perl v5.38 or later:

   use Syntax::Operator::Elem;

   if($x elem @some_strings) {
      say "x is one of the given strings";
   }

Or on Perl v5.14 or later:

   use v5.14;
   use Syntax::Operator::Elem qw( elem_str );

   if(elem_str $x, @some_strings) {
      say "x is one of the given strings";
   }

=head1 DESCRIPTION

This module provides infix operators that implement element-of-list tests for
strings and numbers.

Support for custom infix operators was added in the Perl 5.37.x development
cycle and is available from development release v5.37.7 onwards, and therefore
in Perl v5.38 onwards. The documentation of L<XS::Parse::Infix>
describes the situation in more detail.

While Perl versions before this do not support custom infix operators, they
can still be used via C<XS::Parse::Infix> and hence L<XS::Parse::Keyword>.
Custom keywords which attempt to parse operator syntax may be able to use
these.

Additionally, earlier versions of perl can still use the function-like
wrapper versions of these operators. Even though the syntax appears like a
regular function call, the code is compiled internally into the same more
efficient operator internally, so will run without the function-call overhead
of a regular function.

=cut

sub import
{
   my $pkg = shift;
   my $caller = caller;

   $pkg->import_into( $caller, @_ );
}

sub unimport
{
   my $pkg = shift;
   my $caller = caller;

   $pkg->unimport_into( $caller, @_ );
}

sub import_into   { shift->apply( 1, @_ ) }
sub unimport_into { shift->apply( 0, @_ ) }

sub apply
{
   my $pkg = shift;
   my ( $on, $caller, @syms ) = @_;

   require Syntax::Operator::In;  # no import

   @syms or @syms = qw( elem ∈ );

   $pkg->XS::Parse::Infix::apply_infix( $on, \@syms, qw( elem ∈ ) );

   my %syms = map { $_ => 1 } @syms;
   my $callerpkg;

   foreach (qw( elem_str elem_num )) {
      next unless delete $syms{$_};

      $callerpkg //= meta::package->get( $caller );

      $on ? $callerpkg->add_symbol( '&'.$_ => \&{$_} )
          : $callerpkg->remove_symbol( '&'.$_ );
   }

   croak "Unrecognised import symbols @{[ keys %syms ]}" if keys %syms;
}

=head1 OPERATORS

=head2 elem

   my $present = $lhs elem @rhs;

Yields true if the string on the lefthand side is equal to any of the strings
in the list on the right.

Note that it is specifically B<not> guaranteed that this test will be
performed in any particular order. Nor is it guaranteed that any C<eq>
operator overloading present on any of the elements is respected. These
conditions may allow an implementation at least partially based on a hash,
balanced binary tree, or other techniques.

=head2 ∈

   my $present = $lhs ∈ @rhs;

Yields true if the number on the lefthand side is equal to any of the numbers
in the list on the right.

Note that it is specifically B<not> guaranteed that this test will be
performed in any particular order. Nor is it guaranteed that any C<==>
operator overloading present on any of the elements is respected. These
conditions may allow an implementation at least partially based on a hash,
balanced binary tree, or other techniques.

=cut

=head1 FUNCTIONS

As a convenience, the following functions may be imported which implement the
same behaviour as the infix operators, though are accessed via regular
function call syntax.

=head2 elem_str

   my $present = elem_str( $lhs, @rhs );

A function version of the L</elem> stringy operator.

=head2 elem_num

   my $present = elem_num( $lhs, @rhs );

A function version of the L</∈> numerical operator.

=cut

=head1 AUTHOR

Paul Evans <leonerd@leonerd.org.uk>

=cut

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