Pattern Configuration

It is sometimes useful to permit the end-user to modify certain characteristics of a pattern, such as whether to enable features that might be costly, or to change a set of default paths or package names. This is enabled with pattern configuration blocks. Pattern configuration is new in TPL 1.2.

The following topics are covered in this section:

Configuration block definition

configuration blocks are top-level elements. Like other elements, they have a name and a version number. Pattern modules can import configuration blocks from other modules, using the usual version numbering conventions.

The form of a configuration block is:

configuration name version
  """
  Description of configuration block to show in UI
  """

  "Description of first configuration item"
  config_name := config_value;

  ...
end configuration;

Configuration items are given a human-readable description to be shown in the user interface, an identifier to use in patterns, and a default value. The default value is the value used if the configuration item has not been changed by the user. It also determines the type of the configuration item — the user interface will only allow the user to change the setting to a value with the same type. The valid types for configuration items are text string, integer, boolean, list of strings, and list of integers.

This example shows a number of configuration settings:

configuration MyConfig 1.0
  """
  An example configuration block.
  """

  "A boolean flag"
  a_flag := true;

  "Command to run"
  command := "sudo rm -rf /";

  "Port for the service"
  port := 12345;

  "Paths to look in"
  paths := [ "/usr/bin", "/usr/local/bin" ];

end configuration;

Using configuration settings

Configuration settings are used in patterns by giving the scoped name of the configuration block, followed by the configuration setting name:

if MyConfig.a_flag then
  result := discovery.runCommand(host, MyConfig.command);
end if

Types of default empty lists

The types of configurations items can usually be inferred from the type of the default value. However, if the default value of a configuration item is an empty list, the system cannot know whether it is a list of text strings or a list of integers. To tell the system the type of such a configuration item, an example of the type should be provided in parentheses after the empty list:

"This is a list of strings that's empty by default"
empty_string_list := [ ] ("");

"This is a list of integers that's empty by default"
empty_number_list := [ ] (0);