Layouts

There are four different kind of layout definitions in TreeLDR:

Empty Layout

The empty layout is defined by simply declaring the name of the layout directly followed by a semicolon.

// Empty layout.
layout MyLayout for MyType;

Structure Layout

A structure layout is a list of fields each bound to a property of the layout's type.

// Structure layout.
layout MyLayout for MyType {
	property1 as fieldName1: Layout1,
	// ...
	propertyN as fieldNameN: LayoutN
}

The layout of each field is specified after a colon : using a layout expression.

Enumeration Layout

[To Do]

Layout Alias

Lastly, it is possible to define layout aliases. Such a layout is defined using a layout expression.

layout MyLayout = LayoutExpression;

Layout Expression

A layout expression is a composition of existing layouts by union, intersection, and restriction.

Union

The union between two or more layouts is expressed using the | operator.

LayoutA | ... | LayoutN

Under the hood, this implicitly defines an enumeration layout.

Intersection

The intersection between two or more layouts is expressed using the & operator.

LayoutA & ... & LayoutN

Range Restriction

Range restrictions are used to select a subset of a layout by restricting the range of one of its fields. Just like with types, there are two kinds of range restrictions: universal and existential.

A universal range restriction is built using the all keyword:

all someProperty as fieldName: RestrictedLayout

This denotes the layout of all instances such that all values of fieldName are instances of RestrictedLayout.

Similarly, the existential range restriction is built using the any keyword:

any someProperty as fieldName: RestrictionLayout

This denotes the layout of all instances such that at least one value of fieldName is an instance of RestrictedLayout.

Range restrictions are usually part of an intersection:

Layout & all someProperty as fieldName: RestrictionLayout