Learning lambdas and functions

Functions have long been an essential part of Puppet. Due to the new type system, a complete new set of functions have been possible—functions with different behavior based on parameter data types.

To understand functions, we first have to take a look at lambdas, which are introduced in Puppet 4. Lambdas represent a snippet of Puppet code, which can be used in functions. Syntactically, lambdas consist of an optional type and at least one variable with optional defaults set, enclosed in pipe signs (|) followed by Puppet code inside a block of curly braces:

$packages = ['htop', 'less', 'vim']
each($packages) |String $package| {
      package { $package:
    ensure => latest,
  }
}

Lambdas are typically used on functions. The preceding example uses the each function on the $packages variable, iterating over its contents, setting the lambda variable $package within each iteration to the values htop, less, and vim, respectively. The Puppet code block afterwards...