Syntax Definition Formalism

The Syntax Definition Formalism (SDF) is a metasyntax used to define context-free grammars: that is, a formal way to describe formal languages. It can express the entire range of context-free grammars. Its current version is SDF3. A parser and parser generator for SDF specifications are provided as part of the free ASF+SDF Meta Environment. These operate using the SGLR (Scannerless GLR parser). An SDF parser outputs parse trees or, in the case of ambiguities, parse forests.

Overview

Features of SDF:

• Supports the entire range of context-free languages
• Allows modular syntax definitions (grammars can import subgrammars) which enables reuse
• Supports annotations

Examples

The following example defines a simple Boolean expression syntax in SDF2:

module basic/Booleans

exports sorts Boolean context-free start-symbols Boolean

context-free syntax "true" -> Boolean "false" -> Boolean lhs:Boolean "|" rhs:Boolean -> Boolean {left} lhs:Boolean "&" rhs:Boolean -> Boolean {left} "not" "(" Boolean ")" -> Boolean "(" Boolean ")" -> Boolean

context-free priorities Boolean "&" Boolean -> Boolean > Boolean "|" Boolean -> Boolean

Program analysis and transformation systems using SDF

• ASF+SDF Meta Environment provides SDF
• RascalMPL
• Spoofax/IMP http://strategoxt.org/Spoofax
• Stratego/XT
• Strafunski

See also

• GNU bison
• ANTLR

References

Further reading

• A Quick Introduction to SDF, Visser, J. & Scheerder, J. (2000) CWI
• The Syntax Definition Formalism SDF, Mark van den Brand, Paul Klint, Jurgen Vinju (2007) CWI

External links

• Grammar Deployment Kit
• SdfMetz computes metrics for SDF grammars
• Download SDF from the ASF+SDF Meta Environment homepage