Overview
The SDF syntax definition formalism allows a concise and natural
expression of the syntax of a context-free language. SDF integrates
lexical and context-free syntax in a single syntax formalism. The
complete syntax of a language is thus defined in a single
definition. SDF supports arbitrary context-free grammars. Therefore,
SDF does not restrict the grammars to a subclass of the context-free
grammars, such as LL or LALR. SDF syntax definitions can be
modular. SDF modules can be reused in different syntax
definitions. Disambiguation of grammars is not done by grammar
hacking, but by applying special purpose disambiguation facilities in
SDF, such as priorities, reject productions, and follow restrictions.
SDF is a declarative language. This means that a syntax definition can
be used for different purposes then the usual application: the
generation of a parser. Instead, SDF syntax definitions can be used
to generate other tools from syntax definitions, e.g. pretty-printers
and data type definitions.
Language Features
- Modules
- Integration of lexical and context-free syntax
- Character classes
- Regular expressions
- Disambiguation by relative priorities
- Disambiguation by associativity
- Aliases
- Renaming and parameterization of modules
- Lookahead restrictions
- Reject productions
Design Features
Implementers of SDF2 will appreciate its orthogonality. Language
features are defined, as much as possible, orthogonal with respect to
each other. Despite providing a rich formalism at the level of the
user language, the implementation only has to work on a small kernel
formalism to which syntax definitions are transformed. Most features
are expressed by a translation to the kernel formalism, which is
performed by the SDF normalizer.
All symbols are first-class. For example, symbols can be used at the
right-hande side of a production. This means that it is possible to
define production rules that construct lists of symbols, optional
symbols, and even literals.
Implementation Features
- Parser generation: SLR1 with special treatment of priorities