NAME

Data::Monad::Either - The Either monad

SYNOPSIS

  use Data::Monad::Either qw/left right/;
  sub get_key {
    my ($key) = @_;
    return sub {
      my ($data) = @_;
      return left('value is not a hash') unless ref($data) eq 'HASH';
      return exists($data->{$key}) ? right($data->{$key}) : left("data has no values for key:$key");
    };
  }

  my $commit_data = { commit => { author => 'Larry' } };
  my $right = right($data)->flat_map(get_key('commit'))->flat_map(get_key('author'));
  $right->value; # => 'Larry'

  my $not_hash = right(['Larry'])->flat_map(get_key('commit'))->flat_map(get_key('author'));
  $not_hash->value; # => 'value is not a hash'

  my $not_exists_key = right($data)->flat_map(get_key('parent_commit'))->flat_map(get_key('author'));
  $not_exists_key->value; # => 'data has no values for key:parent_commit'

DESCRIPTION

Data::Monad::Either represents values with 2 possibilities.

METHODS

$right = right(@values)

$left = left(@values)

The constructors of this class.

$bool = $either->is_right

$bool = $either->is_left

Checks if $either is right (correct) or left (failure)

$either->unit(@values)

$either->flat_map(sub { })

Overrides methods of Data::Monad::Base::Monad

@values = $either->value

Returns a list of values which is contained by $either

$folded = $either->fold(sub { ... }, sub { ... });

Run the first function if left, or the second.

These given functions take a value contained by $either.

$either_or = $either->or_else($else);

Returns this Either monad if it is right, or returns the given value.

$get_or_else = $either->get_or_else(@value_else);

Returns the values contains by this, or returns the given default value.

$value_or = $either->value_or(sub { ... });

Returns the values contains by this, or runs the given default function on the left value.

$swapped = $either->swap;

Flip the left right values.

$either = $either->left_map(sub { ... });

Run the given function on the left value.

AUTHOR

aereal <aereal@aereal.org>

SEE ALSO

Data::Monad::Base::Monad

LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.