A language is a named collection of rules for imposing structure on text.
LanguageDeclaration: Attributesopt language Name LanguageBody LanguageBody: { RuleDeclarationsopt } RuleDeclarations: RuleDeclaration RuleDeclarations RuleDeclaration
The language that follows recognizes the single text value "Hello World":
module HelloWorld {
language HelloWorld {
syntax Main
= "Hello World";
}
}A language may consist of any number of rules. The following language recognizes the single text value "Hello World":
module HelloWorld {
language HelloWorld {
syntax Main
= Hello Whitespace World;
token Hello
= "Hello";
token World
= "World";
token Whitespace
= " ";
}
}The three rules Hello, World, and Whitespace recognize the three single text values "Hello", "World", and " " respectively. The rule Main combines these three rules in sequence. The difference between syntax and token rules is described in Section 11.1.
Main is the distinguished start rule for a language. A language recognizes a text value if and only if Main recognizes a value. Also, the output for Main is the output for the language.
Rules are members of a language. A language can use rules defined in another language using member access notation. The HelloWorld language recognizes the single text value "Hello World" using rules defined in the Words language:
module HelloWorld {
language Words {
token Hello
= "Hello";
token World
= "World";
}
language HelloWorld {
syntax Main
= Words.Hello Whitespace Words.World;
token Whitespace =
= " ";
}
}All rules defined within the same module are accessible in this way. Rules defined in other modules must be exported and imported as defined in the next chapter.