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
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Outline
Layout Expression