GDL Constructs

A GDL construct is simply a GDL attribute followed by a construct body. Logically, a construct represents a collection of data, much like a C structure does.

A construct body is zero, one, or more GDL entries enclosed by construct delimiter characters. The construct body must be introduced by the left curly brace ({), and terminated by the right curly brace (}).

The GDL entries that are enclosed by the construct delimiter characters are referred to as the contents of the construct. The enclosed GDL entries are also referred as children, child entries, child elements, or members of the construct. Because the child entries can also be constructs, you can create arbitrarily deep nestings of constructs; however, only the immediate descendants of the parent construct are called child entries.

Conversely, the construct that immediately encloses the child entries is sometimes referred as the parent construct. Two GDL entries that share the same parent construct are called Siblings. A construct whose body contains the parent of an entry or the parent of a parent of an entry (and so on) is called an ancestor construct.

The attribute that precedes the construct body is called the construct head, or sometimes just the construct. The keyword component of the construct head is called the construct type. If multiple sibling constructs are defined, each with the same keyword, they are considered to belong to the same construct type. The value component of the construct head is called the construct instance name, or the construct tag. The construct tag is expected to be a symbol. The construct tag is syntactically optional but is required in some cases.

Constructs can be either syntactical or logical. Constructs can consist of unions.

An arbitrary amount of whitespace and linebreak sequences can precede or follow the construct delimiter characters. However, for the sake of readability, a C-style indentation convention is typically used.

The following code example shows a GDL construct.

*ConstructType: ConstructTag
{   *%  Begin Construct Delimiter
*%  this is the Construct Body
*ChildAttribute: child attribute value
*ChildConstruct: ChildConstructTag
{
 *%  Body of Child construct could hold more constructs.
}
*AnotherChildConstruct: ChildConstructTag2
{
 *% Contents of *AnotherChildConstruct
 *% since both child constructs share the same Parent construct, they are
 *% Sibling Constructs.
 *DescendantAttribute:  this attribute is a descendant of  *ConstructType: ConstructTag
}
}   *%  End Construct Delimiter

This section includes:

GDL Construct Delimiters

Syntactical and Logical Constructs in GDL

GDL Construct Unions

GDL Whitespace Characters

GDL Comments

GDL Strings