Freon Documentation (version 0.5.0)

Our Philosophy

The design philosophy that we follow in Freon can best be described by the following quote from the well-known graphical user interface designer Alan Kay.

Simple things should be simple, complex things should be possible. (Alan Kay, Turing Award Winner)

The Pareto Principle

Freon is a minimal viable product which supports the language engineer in creating a work environment for a mini-language. A key principle is the Pareto principle (or 80%-20% rule), which states that for many events, roughly 80% of the effects come from 20% of the causes. For example, it is an axiom of business management that “80% of sales come from 20% of clients”.

In software development the Pareto principle translates to “80% of the development effort is spent on 20% of the application”, this 20% being the more complex parts. Still, the other 80% of the application needs to be created as well.

Freon aims to make the latter as simple as possible, while keeping the generated code open for the language engineer to code the more complex parts by hand. One of our use cases is the creation of a prototype language in a day or in a couple of days at most.

Other Guidelines

Other guidelines have been ease of use, and flexibility. Freon may not (yet OOPS) do everything you need, but what it does, should be very easy to get into. Furthermore, Freon is designed to be extendable, and easy to integrate with other tooling. In practise this means that:

  • Every part of the work environment that is generated, can be exchanged for one that suits the language engineer better, provided the right interface is implemented.
  • Every part of the work environment is made by its own generator, so you can adjust which parts you want to generate and which parts you omit.
  • The different parts of the work environment can be run on either the server or the client. Thus creating multiple deployment options.

With these principles in mind, we have started of small and simple. Every definition language, from the language structure to the validation rules, is kept minimal. Over time, in an agile fashion, these will be extended whenever the need arises.

Furthermore, we intend to use bootstrapping in one of the next versions of Freon to create editors for every one of the definition languages. If you are interested, you can check out our wish list of features to be developed in the future.

Name-Based References

In Support for Expressions we explain that editing expressions is a known challenge for projectional editors. A second challenge is posed by references, which is stated in Efficiency of Projectional Editing: A Controlled Experiment as follows.

References. References are based on pointers to the targetnode’s ID. Despite some advantages (e.g., robust refactorings) of this approach, we observe problems with the tradeoff that the reference target has to exist at the time the reference is created. A more robust and intuitive handling of references is desirable. While some problems can be solved by language developers (e.g., quick fixes to create reference targets), there should be a better way to support references by the IDE itself.

[Markus Voelter a.o., Efficiency of Projectional Editing]

This is the reason that in Freon we allow only name-based references, which are resolved on a need-to basis. Every reference is an instance of the class PiElementReference, which holds:

  • the name or path (i.e. a list of names) of the referred element
  • the meta-type of the referred element
  • a cache of the element itself

This means that the AST is truly a tree, not a graph. One advantage is that we are not obliged to have the complete model in memory. Our use of multi-file models is explained in Models and Model Units.