The Fortress Language Specification - CiteSeerX

sql
SELECT spectral class FROM stars
end
would be expanded into the following Fortress SyntaxTree:
Call(Empty,
List(VarRef(Identifier(“SqlQuery”)),
Call(Empty,
List(VarRef(Identifier(“Select”)),
String(“spectral_class”))),
Call(Empty,
List(VarRef(Identifier(“From”)),
String(“stars”)))))
(The Empty lists passed to Calls are the lists of static parameters to these calls). Note that this SyntaxTree corresponds
to the following Fortress concrete syntax:
SqlQuery(Select(“spectral_class”), From(“stars”))
36.2 Declarations of Syntax Expanders
Syntax:
AbsDecl ::= AbsExternalSyntax
AbsExternalSyntax ::= syntax OpenExpander Id CloseExpander
A declaration of a syntax expander is syntactically identical to the definition of a syntax expander, except that =
and the body of the expander (i.e., the expression following the = sign in an expander definition) are elided. Syntax
expander declarations must occur only in APIs. A component that exports an API A must provide, for each syntax
expander declaration d in A, a syntax expander definition with a header identical to d.
36.3 Restrictions on Delimiters
Consider the set S of syntax expander declarations imported by a component or API B, along with the syntax expanders
defined or declared in B directly. Every expander in S must have a distinct opening delimiter, or it is a static
error. Moreover, the terminating delimiter of each syntax expander must be distinct from every opening delimiter of
every syntax expander in S, or it is a static error.
36.4 Processing Syntax Expanders
In a given component, only syntax expander declarations appearing in APIs imported by the component may be used.
A component exporting an API A that includes a syntax expander must not import APIs that are not also imported by
A, or it is a static error. This restriction ensures that all names in scope of the definition of the syntax expander are also
in scope of any component importing the syntax expander in A. Additionally, all use sites of a syntax expander must
occur in simple components other than the defining component. Furthermore, multiple components containing syntax
expanders must not be cyclically linked. These restrictions avoid pathologies with nontermination during expansion.
Finally, to maintain proper separation of test code, a syntax expander definition is statically forbidden from referring
to variables or functions that have modifier test .
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