PiElement

As Freon uses the AST for projections and behavior, it needs to know about the type of elements in the AST. To allow Freon to work, each element type that occurs in the AST needs to implement the PiElement interface. This interface is kept as small as possible, to allow Freon to be used for any AST.

/* File: core/src/language/PiElement.ts */

export interface PiElement {
	piId(): string;

	piLanguageConcept(): string;

	piContainer(): PiContainerDescriptor;

	piIsModel(): boolean;

	piIsUnit(): boolean;

	piIsExpression(): boolean;

	piIsBinaryExpression(): boolean;
}

The main two elements in this interface are:

• piId(), which should return en unique id for each element in the AST.
• piContainer() which should return a descriptor for the container (parent) of an element in the AST.

The two functions piIsExpression() and piIsBinaryExpression() are only needed when your language contains expressions, as Freon includes special handling of expressions. To start with, these functions can be defined to simply return false.

Note that Freon does not need to know anything about the structure of your language. No need to know the available element type, nor the properties of en element type, nor anything else. This is by design, as Freon is not meant to be a full Language Workbench, but instead meant to be used with multiple language workbenches , or none.