Reference

NOTE

Reference is not yet implemented in the parser.

REAM reference is inspired by YAML's anchor and alias, and is my implementation for this rejected feature for TOML.

Another inspiration for referencing is my wrong understanding of how inheritances work in object-oriented programming. I initially thought inheritances works with instances, and child instances are able to call parent instances' attributes and methods.

It turns out that what I was thinking was similar to a programming paradigm called "environmental acquisition" (Gil & Lorenz, 1995) but there is almost no implementation for it. The only one I could find is the python package Acquisition, and a simple illustration of how it work is as follows:

import ExtensionClass, Acquisition

class Country(ExtensionClass.Base):
    def __init__(self, name):
        self.name = name

class Language(Acquisition.Implicit):
    def __init__(self, name):
        self.name = name

belgium = Country("Belgium")
flemish = Language("Flemmish")

flemish.country = belgium

print(flemish.country.name) # Belgium

belgium is a Country object, and flemish is a Language object. While Language is not a subclass of Country, I can make flemish acquire the attribute name from belgium.

The preliminary design is as follows.

(The syntax highlighting is a bit messed up)

Example 1:

# CountryYear
- country (String): Belgium
- year (String): 2020
- unique_id (fn -> String): `THIS$country + '_' + THIS$year`

The keyword THIS can be omitted if it is followed by a local attribute:

# CountryYear
- country (String): Belgium
- year (String): 2020
- unique_id (fn -> String): `$country + '_' + $year`

Also values that are referenced require explicit typings. The following will raise an error:

# CountryYear
- country (String): Belgium
- year: 2020
- unique_id (fn -> String): `$country + '_' + $year`

Example 2:

# The Benelux Union
- members:
  * Belgium
  * Netherlands
  * Luxembourg
- total_pop (fn -> Number): `THIS::Country$pop.SUM()`

## Country
- name: Belgium
- pop (Number): $11433256$

## Country
- name: Netherlands
- pop (Number): $17332850$

## Country
- name: Luxembourg
- pop (Number): $619900$

Attributes from sub-entries can be referenced by the namespace <SubEntry Name>.

Example 3:

# Country
- name: United States of America
- captial: Washington, D.C.

## City
- name: New York
- is_capital (fn -> Boolean): `THIS$name == THIS::SUPER$capital`

## City
- name: Washington, D.C.
- is_capital (fn -> Boolean): `THIS$name == THIS::SUPER$capital`

Attributes from a parent entry can be referenced by the SUPER namespace.