Syntax::Keyword::WhileEach

Iterator.pm

package Syntax::Keyword::WhileEach::Iterator;

use strict;
use warnings;
use Carp 'croak';
use Scalar::Util 'reftype';

sub new {
  my ($class, $structure) = @_;
  my $reftype = reftype $structure;
  croak 'each requires a hash or array' unless $reftype eq 'HASH' or $reftype eq 'ARRAY';
  my $is_hash = $reftype eq 'HASH';
  my $keys = [$is_hash ? keys %$structure : 0..$#$structure];
  return bless {is_hash => $is_hash, keys => $keys, structure => $structure}, $class;
}

sub next {
  my ($self) = @_;
  return () unless @{$self->{keys}};
  my $key = shift @{$self->{keys}};
  return wantarray
    ? ($key, $self->{is_hash} ? $self->{structure}{$key} : $self->{structure}[$key])
    : $key;
}

1;

WhileEach.pm

package Syntax::Keyword::WhileEach;

# some keyword magic that defines a keyword while_each that rewrites:
# LABEL: while_each (my ($k, $v) = each %foo) { ... }
# to:
# {
#   my $iter = Syntax::Keyword::WhileEach::Iterator->new(\%foo);
#   LABEL: while (my ($k, $v) = $iter->next) { ... }
# }

1;