#  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, 2021 -- leonerd@leonerd.org.uk

package Syntax::Operator::Divides 0.02;

use v5.14;
use warnings;

use Carp;

require XSLoader;
XSLoader::load( __PACKAGE__, our $VERSION );

=head1 NAME

C<Syntax::Operator::Divides> - an infix operator for division test

=head1 SYNOPSIS

On a suitably-patched perl:

   use Syntax::Operator::Divides;

   say "Multiple of 10" if $x %% 10;

Or, on a standard perl via L<Syntax::Keyword::Match>:

   use v5.14;
   use Syntax::Keyword::Match;
   use Syntax::Operator::Divides;

   foreach ( 1 .. 100 ) {
      match( $_ : %% ) {
         case(15) { say "FizzBuzz" }
         case(3)  { say "Fizz" }
         case(5)  { say "Buzz" }
         default  { say $_ }
      }
   }

=head1 DESCRIPTION

This module provides an infix operator that implements an integer divides test
which returns true if the lefthand operand is a whole multiple of the
righthand.

Current versions of perl do not directly support custom infix operators. The
documentation of L<XS::Parse::Infix> describes the situation, with reference
to a branch experimenting with this new feature. This module is therefore
I<almost> entirely useless on standard perl builds. While the regular parser
does not support custom infix operators, they are supported via
C<XS::Parse::Infix> and hence L<XS::Parse::Keyword>, and so custom keywords
which attempt to parse operator syntax may be able to use it. One such module
is L<Syntax::Keyword::Match>; see the SYNOPSIS example given above.

=cut

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

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

sub import_into
{
   my $class = shift;
   my ( $caller, @syms ) = @_;

   @syms or @syms = qw( divides );

   my %syms = map { $_ => 1 } @syms;
   $^H{"Syntax::Operator::Divides/divides"}++ if delete $syms{divides};

   {
      no strict 'refs';
      *{"${caller}::is_divisor"} = \&is_divisor if delete $syms{is_divisor};
   }

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

=head1 OPERATORS

=head2 %%

   my $divides = $numerator %% $denominator;

Yields true if the numerator operand is a whole integer multiple of the
denominator. This is implemented by using the C<%> modulus operator and
testing if the remainder is zero.

=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.

These wrapper functions are implemented using L<XS::Parse::Infix>, and thus
have an optimising call-checker attached to them. In most cases, code which
calls them should not in fact have the full runtime overhead of a function
call because the underlying test operator will get inlined into the calling
code at compiletime. In effect, code calling these functions should run with
the same performance as code using the infix operators directly.

=head2 is_divisor

   my $divides = is_divisor( $numerator, $denominator );

A function version of the L</%%> operator.

=cut

=head1 AUTHOR

Paul Evans <leonerd@leonerd.org.uk>

=cut

0x55AA;
