Writing PCRL

Introduction

Automancer protocols are defined in PCRL, a configuration language close to YAML. It is designed to be lightweight and human-readable. It is also used in setup configuration files.

The extension of PCRL is .pcrl and its media (MIME) type is text/pcrl. The recommended case is snake case, i.e. snake_case.

Examples

The following PCRL:

# A comment

database:
  server: 192.168.1.1
  ports: [8000, 8001, 8002]
  connection_max: 5000
  options: { enabled: true }

servers:
  - name: alpha
    ip: 10.0.0.1
    dc: eqdc10
  - name: beta
    ip: 10.0.0.2
    dc: eqdc10

Maps to the following JSON:

{
  "database": {
    "server": "192.168.1.1",
    "ports": [8000, 8001, 8002],
    "connection_max": 5000,
    "options": {
      "enabled": true
    }
  },
  "servers": [
    {
      "name": "alpha",
      "ip": "10.0.1",
      "dc": "eqdc10"
    },
    {
      "name": "beta",
      "ip": "10.0.2",
      "dc": "eqdc10"
    }
  ]
}

Comparison with YAML

PCRL is conceptually close to YAML and YAML's syntax highlighting definitions can be used to highlight PCRL, such as in snippets embedded within a Markdown file. When taking a closer look, however, YAML and PCRL have major differences:

• Values in PCRL are either a dictionary, a list, a string or null.

  foo: null  # foo is None
  foo: 32    # foo is 32
  foo: false # foo is false
  

• PCRL has no support for nested dictionaries on a single line.

  foo:
    bar: 23
  
  # or
  
  foo: { bar: 23 }
  
  # instead of
  
  foo: bar: 34
  

• PCRL has no support for JSON structures.
• PCRL has no support for anchors and references.
• PCRL has no support for data typing.
• PCRL has no support for multiple documents.
• PCRL only has the | syntax for multiline strings but no support for >.

  key: |
    Not like the brazen giant of Greek fame,
    With conquering limbs astride from land to land;
    ...
  
  # instead of
  
  key: >
    Not like the brazen giant of Greek fame,
    With conquering limbs astride from land to land;
    ...
  

• PCRL enforces two-spaces indentation.
• PCRL requires one more indentation level when dealing with lists of dictionary of lists.

  - a:
      - b
  
  # instead of
  
  - a:
    - b