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.^[1] 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[edit]

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[edit]

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[edit]

• ASF+SDF Meta Environment provides SDF
• RascalMPL
• Spoofax/IMP [1]
• Stratego/XT
• Strafunski

See also[edit]

• GNU bison
• ANTLR

References[edit]

Further reading[edit]

• 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[edit]

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

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