Reduce is used to reduce the array to a single value. This can be used to calculate the maximum or minimum of the array, or in this case, the sum of the elements of the array:

$count = [1,2,3,4,5]
$sum = reduce($count) | $total, $i | { $total + $i }
notice("Sum is $sum")

This preceding code will compute the sum of the $count array and store it in the $sum variable, as follows:

t@cookbook:~/.puppet/manifests$ puppet apply --parser future lambda.pp
Notice: Sum is 15
Notice: Compiled catalog for cookbook.example.com in environment production in 0.36 seconds
Notice: Finished catalog run in 0.03 seconds

Filter is used to filter the array or hash based upon a test within the lambda function. For instance to filter our $count array as follows:

$filter = filter ($count) | $i | { $i > 3 } notice("Filtered array is $filter")

When we apply this manifest, we see that only elements 4 and 5 are in the result:

Notice: Filtered array is [4, 5]

Map is used to apply a function to each element of the array. For instance, if we wanted (for some unknown reason) to compute the square of all the elements of the array, we would use map as follows:

$map = map ($count) | $i | { $i * $i } notice("Square of array is $map")

The result of applying this manifest is a new array with every element of the original array squared (multiplied by itself), as shown in the following command line output:

Notice: Square of array is [1, 4, 9, 16, 25]

Slice is useful when you have related values stored in the same array in a sequential order. For instance, if we had the destination and port information for a firewall in an array, we could split them up into pairs and perform operations on those pairs:

$firewall_rules = ['192.168.0.1','80','192.168.0.10','443']
slice ($firewall_rules,2) |$ip, $port| { notice("Allow $ip on $port") }

When applied, this manifest will produce the following notices:

Notice: Allow 192.168.0.1 on 80
Notice: Allow 192.168.0.10 on 443

To make this a useful example, create a new firewall resource within the block of the slice instead of notice:

slice ($firewall_rules,2) |$ip, $port| { firewall {"$port from $ip": dport  => $port, source => "$ip", action => 'accept', }
}

Each is used to iterate over the elements of the array but lacks the ability to capture the results like the other functions. Each is the simplest case where you simply wish to do something with each element of the array, as shown in the following code snippet:

each ($count) |$c| { notice($c) }

As expected, this executes the notice for each element of the $count array, as follows:

Notice: 1
Notice: 2
Notice: 3
Notice: 4
Notice: 5

There are other new features of Puppet language available when using the future parser. Some increase readability or compactness of code. For more information, refer to the documentation on puppetlabs website at http://docs.puppetlabs.com/puppet/latest/reference/experiments_future.html.